The Unicorn and the Wasp ( TV story ) The Unicorn and the Wasp was the seventh episode of the fourth series of " Doctor Who " . It saw " Doctor Who " s take on the disappearance of famous author Agatha Christie in 1926 . This also marks the third time the Doctor has had an adventure with in the revived series with a famous author . It also featured some kind of threatening creature related to said author ' s works . It ' s mentioned again that bees have been vanishing from Earth in 2009 . This served as a link to the Missing Planets Arc ; the inclusion of the Vespiform race in this episode was to serve as a big hint that the bees would actually have something to do with the end of the arc . Synopsis . In 1926 , Agatha Christie mysteriously disappears , only to be found ten days later at Harrogate Hotel with no memory of what happened to her . What could have been the cause ? Was it a nervous breakdown ? Was it a cry for help ? Or did it involve a giant alien wasp and a mysterious stranger known only as the Doctor ? Plot . The TARDIS materialises outside a country estate , hidden by trees ; the Tenth Doctor and Donna Noble step out . The Doctor smells the air ( which has the scent of mint and lemonade ) and tells Donna that they have landed in the 1920s . Donna wonders if the Doctor really could tell the year by smell ; he tells her it ' s true . However , she then points out that the vintage car coming up the driveway may have given it away . They both hide . The car ' s driver , Professor Peach , parks outside the house . He is promptly greeted by his old friend , the butler Greeves , just as the local reverend , Arnold Golightly , arrives on his bicycle . As the servants take their luggage , they exchange a few words . Peach decides to go to the library to do some research on his own . Golightly tells Professor Peach that they ' re at a party , he should try to relax ; constantly working will be the death of him . Watching from the side of the house , Donna tells the Doctor to forget about planet Zog — a party in the 1920s is much more fun . The Doctor tells her that the trouble is that they haven ' t been invited ; however , then pulls out the psychic paper , saying " oh , right . Yes , were are ! " . Donna heads back into the TARDIS to find a dress from the 1920s to wear for the party . In the library , Professor Peach looks at one document and realises that he was right about something kept secret all these years . Suddenly , a shadowy person comes in , and Peach quickly hides his papers , telling the person that he was just doing some mundane research . He then asks the mysterious person what he is doing with a lead pipe . The mysterious person ' s eyesight becomes purple as Peach mumbles , " That ' s impossible ! " . The mysterious person , revealed to be a giant wasp , suddenly swings the piece of pipe at Peach ' s head as the Professor screams . . . Back outside , the Doctor is impatiently waiting outside the TARDIS for Donna to finish changing into proper attire , reminding her that they ' ll be late for cocktail s . Donna comes out in a period dress and with her hair done up and asks , " What do you think ? Flapper or slapper ? " The Doctor smiles and responds , " Flapper . You look lovely . " They head for the front lawn . They are greeted by Lady Clemency Eddison , who wonders who they are . The Doctor uses the psychic paper to fake an invite and comes up with a story about meeting her at an ambassador ' s reception . Lady Eddison excuses herself as she is being cautious because the Unicorn is about . The Doctor , at first , mistakes this for an actual unicorn before Lady Eddison clears up the confusion by explaining that " the Unicorn " is a notorious jewel thief who is on the loose and has just struck again . Next , they meet Lady Eddison ' s wheelchair - bound husband , Colonel Hugh Curbishley , and their son Roger , who starts to hit on Donna ; the Colonel has been in his wheelchair since 1918 due to a terrible illness . Donna is confused why Lady Eddison has a different surname and the Doctor explains that the Eddison title descends through Lady Eddison , not the Colonel ; one day Roger will be a lord . Roger secretly flirts with Davenport , the male servant ; Donna and the Doctor easily pick up on the homosexual relationship between them and whisper quips to each other . ( Donna says , " All the decent men are on the other bus , " to which the Doctor adds , " Or Time Lord s . " ) Next to arrive is Reverend Golightly , whom Lady Eddison congratulates on the apprehension of two boys who tried robbing his church last Thursday night . Following him is the socialite Robina Redmond . Last to come is British mystery writer , Agatha Christie . The Doctor is ecstatic about meeting her , as she is another of his favourite authors . He admits that he was only surprised once by her books , but " It was a good once ! " . Still a young writer at this point , she has recently published her sixth novel . The Doctor and Donna are both impressed when she calmly notices that they ' re not married , as Donna has no wedding ring . Agatha is , however , unwilling to talk about her husband , who will not be joining them . Seeing that they are a person short , Lady Eddison tells Miss Chandrakala to go into the house and find Professor Peach . Golightly mentions that Peach said he was going to the library ; when Miss Chandrakala investigates the library , her face changes to a look of horror . . . The Doctor acquires a newspaper from Hugh ' s chair and reads it . He immediately realises that something is wrong when he shows Donna the date — 8 December 1926 , the day Agatha Christie disappeared . He explains that Agatha has just discovered that her husband is having an affair . Being British , these people would normally just carry on ( with stiff upper lips ) , but this time , that won ' t happen . Tomorrow morning , her car will be found abandoned by the side of a lake ; ten days later , Agatha will turn up in a hotel in Harrogate with no memory of what happened . She never spoke about what happened to the day she died . A surprised Donna then asks the Doctor , " Then it ' s about to happen . . . " ; he finishes " . . . right here , right now . " Their train of thought is interrupted when Miss Chandrakala comes running back , yelling frantically that the Professor has been murder ed in the library ! The Doctor and Donna race to the library to find the Professor ' s body , followed by Agatha . The Doctor determines that blunt force trauma was the likely cause of death , and notes that the watch broke as the victim fell — pinpointing the exact time of death to 4 : 15 PM . Agatha discreetly takes a piece of paper from the fireplace , but the Doctor notices her reflection in the bookcase . Donna softly asks the Doctor if he noticed the professor ' s murder is like the board game " Clue do " . The others arrive on the scene , and decide to call the police . However , the Doctor uses his psychic paper to identify himself as Chief Inspector Smith of Scotland Yard ( aka " the Doctor " ) and Donna as " the plucky young girl who helps me out " . Donna takes issue with this description , but the Doctor explains that there are no policewomen in 1926 . While Agatha keeps the others in the sitting room until he ' s ready to question them , Donna asks the Doctor why they aren ' t calling the real police . He explains that he has found " morphic residue " — a by - product of shape - shifting — on the floor . This means that one of the others is an alien in human form . Donna then says the situation is weird ; Agatha Christie wasn ' t literally surrounded by murder . She compares it to Charles Dickens being surrounded by ghost s at Christmas . The Doctor hints he actually experienced that , as Donna then asks if they could " drive cross country and find Enid Blyton having tea with Noddy " , before asking if Noddy is real . The Doctor confirms he isn ' t , then rushes off . While the Doctor tastes the residue to determine what left it , they walk past the sitting room . Donna then asks if it ' s like " Murder on the Orient Express " , where everyone did it . Agatha overhears this and finds the idea brilliant . Donna tries to tell her it ' s one of her best books , but the Doctor quietly hints to her that it hasn ' t actually been written yet , so Donna takes advantage of this to get it copyrighted in her name . The Doctor explains he and Agatha will question the suspects , handing Donna a magnifying glass to search the rooms upstairs for clues ( and , he whispers , more residue ) . The Doctor expresses joy at being able to solve a murder mystery with Agatha . She reluctantly agrees to work with him , unhappy at the Doctor ' s casual attitude toward the murder . During the interviews , the guests recount their stories of what they were doing at 4 : 15 PM . Each is revealed to be hiding something , except for Reverend Golightly ( who claims to have been unpacking in his room ) . Lady Eddison claims to having been taking tea ( she was surreptitiously consuming liquor ) . Robina Redmond claims to have been using the toilet ( she was in the bathroom loading a tiny pistol ) . Roger Curbishley claims to have been walking alone ( he was actually having a tryst with his lover Davenport , one of the servants ) . Colonel Hugh claims he was reading military memoirs in the study ( he was actually viewing pornography and fantasising about can - can dancers - which causes him to slip into a second flashback ) . The Doctor manages to snap him out of it , much to Hugh ' s embarrassment . Agatha points out that they have nothing to go on , mentioning they need to use " ze little grey cells " . This prompts the Doctor to talk about his fondness for the character of Poirot , which then causes him to remembering being in Belgium once to rescue Charlemagne from an insane computer . Agatha snaps him out of this flashback and he apologises . She then points out Charlemagne lived centuries ago . The Doctor tells her that he has a very good memory , before being told he missed an important clue . The Doctor then sarcastically asks if it ' s the bit of paper she nicked from the fireplace , explaining that he saw her . Agatha is surprised by the Doctor having noticed this , calling him a " crafty man " , much to his amusement . Agatha produces the paper she removed earlier with the letters " a - i - d - e - n " , preceded by one illegible letter . It obviously spells " maiden " , although neither she nor the Doctor is able to divine its significance . They hope Donna will be able to bring them more clues . Meanwhile , Donna has come upon a locked door during her part of the investigation . She encounters Greeves , who informs her that Lady Eddison has kept the room shut for the last 40 years , after spending six months in it recovering from malaria following her return from India . With Donna pulling rank on him as an investigator from Scotland Yard , Greeves has no choice but to open the door for her . She then dismisses him . Inside the room , it is bare except for a solitary child ' s teddy , making Donna wonder even more why it has been sealed . She then hears a buzzing from the window , commenting that the 1920s , unlike her own time , still had bee s . . . When she pulls back the curtain , instead of a trapped and harmless bee there is a ridiculously giant wasp outside the window . The wasp breaks in and tries attacking her , as Donna backs up to the window . Donna begins yelling for the Doctor , who would know what to do against this thing . Using the magnifying glass , Donna burns the wasp with the sun ' s rays , allowing her to run outside just as the wasp impales its stinger in the door . The Doctor and Agatha arrive , asking what she was yelling for . Donna tells the Doctor that she encountered a giant wasp , piquing the Doctor ' s curiosity . Agatha dismisses the idea , thinking she was scared away by a normal , tiny insect . Donna defends herself with her usual gusto : " When I say ' giant ' , I don ' t mean ' big ' ; I mean " flippin ' enormous ! " " , pointing to the giant stinger still embedded in the door . The Doctor opens the door to find that the wasp has " buzzed off " . Agatha tries to touch the stinger , but the Doctor tells her not to do so . He takes out a vial and pencil to collect a sample . He tells them that there " are " plenty of alien insects , but none should be in this galactic vector . Agatha understands some of the Doctor ' s words , but now thinks he ' s insane . Donna asks the Doctor if the wasp was harmless without its stinger is gone . The Doctor tells her that because of its size , the wasp will be able to grow a new one . Agatha then tells him that there is no such thing as giant wasps . The Doctor tells her that she is right , but points out the question is " why " it ' s here . In the kitchen , Davenport is speculating about the murder with another of the servants while cooking dinner , wondering who would want to kill Professor Peach . The other servant , Mrs . Hart , speculates that it ' s what happens when a party is thrown by the rich and famous . Miss Chandrakala , who is there , dismisses the idea , telling them to get back to work . However , she then has an epiphany , realising exactly " what " Professor Peach had discovered in the library when he was murdered . Miss Chandrakala tells them that she must speak to Lady Eddison and rushes outside to find her . However , a figure watches from above and knocks over a stone gargoyle from the ledge . It lands on Miss Chandrakala with a loud thud . Hearing the thud and Miss Chandrakala ' s cry , the Doctor , Agatha , and Donna rush outside to find her slipping away . As she dies , Miss Chandrkala leaves them with a cryptic message : " The poor little child . . . " Seeing the wasp hovering above the building , the Doctor , Donna and Agatha give chase . Donna notes how the roles are reversed this time ( they ' re chasing the monster now ) . Agatha is still in denial about the wasp being real , thinking it ' s some kind of illusion done with mirror s . They find it coming in through a skylight . The Doctor tries reasoning with it , before they barely dodge an attack . Donna gets the wasp ' s attention and holds up the magnifying glass to threaten it with another shot of focused sunlight . It flies into the next hall as the Doctor yells for them to hurry , and not let it return to human form . Entering the hallway , the Doctor shouts , " There ' s nowhere to run . Show yourself ! " All of the doors open and every suspect appears , looking confused , leading the Doctor to protest " That ' s just cheating ! " . Everyone gathers in the sitting room , where they pressure Agatha to solve the murders . However , she tells them that she is only a writer ; the Doctor is their best chance at solving the case now . She retreats to the garden . Donna follows her to try to restore her confidence . Agatha sadly admits having found her husband with another ( younger ) woman . Donna compares that with her own trouble with men . She also suggests that someday Agatha ' s books may be turned into talking films , before realising her gaffe . Agatha , however , thinks that her books may fade out of interest over time , and she will be forgotten . She then notices a box nearby that has crushed some flowers . Donna points out that nobody else would have noticed that . They take the box to the Doctor , who is in the sitting room . The contents are full of a thief ' s tools , and they suspect that the Unicorn is one of the guests . Greeves arrives and gives them their drinks . Donna asks the Doctor what he found out about the venom from the stinger . Taking out the vial , the Doctor explains that the venom comes from a Vespiform , a race of aliens who have hives in the Silfrax Galaxy . However , the question remains as to why it ' s on Earth and acting like a character out of one of Agatha ' s books . Donna then asks Agatha what Miss Marple would do , pointing out the character ' s M . O . before again realising that she has given yet another idea to Agatha . Donna decides to have Agatha copyright Miss Marple to both of them . The Doctor then calls to Donna with a blank face , saying something is inhibiting his enzymes . He suddenly begins convulsing in pain ; someone has poisoned his drink . Agatha smells the drink , deducing from the telltale scent of bitter almonds that the poison is cyanide . The Doctor rushes to the kitchen , frantically asking for ginger beer . Upon finding a bottle , he drinks some and then pours the rest on himself . Agatha tells him that as an expert in poisons , she knows cyanide is fatal . The Doctor points out that he ( being a Time Lord and non - human ) can stimulate the inhibited enzymes into reversal , thus curing himself . He next asks for protein , and is given walnut s . Then he mimes ( very badly ) a need for salt ; when Donna tries to give him a bag of salt , he says pure salt is " too salty " , so Agatha gives him a bottle of anchovies . Finally , he says he needs a big shock . Promptly , Donna kiss es him . The Doctor exhales the poison in a cloud of smoke , saying he should detoxify more often . Agatha is flabbergasted , exclaiming , " Doctor , you are " impossible " ! Who are you ? " Thunder and lightning have arrived by nightfall . As they are all seated in the dining room , the Doctor points out that they are still having dinner even thought two people have died . Lady Eddison asks what he would want them to do ; being British , they carry on . The Doctor then tells the guests that one of them has failed to poison him . Any one of them could have put cyanide in his drink . He then mentions it gave him an idea . When Golightly asks what it is , the Doctor responds , " Well , poison . " , causing the guests to immediately cease eating . He tells everyone the soup has been laced with pepper . Colonel Hugh finds the extra spice delightful , but the Doctor explains that the active ingredient in pepper is piperine , traditionally used as an insecticide . At that moment , there is a flash of lightning and a thunderclap . A sudden gust of wind blows open the windows , and the candles go out . The Doctor asks the startled group to listen , and sure enough , the wasp ' s buzzing becomes audible again . Lady Eddison exclaims , " No . . . it can ' t be ! " Agatha , meanwhile stands up and calls , " Show yourself , demon ! " It does , above a painting , and the guests flee the dining room with Greeves pulling Donna to safety . The Doctor , Greeves , Donna and Agatha end up in the same room , just outside the dining room . The Doctor takes a sword from a nearby coat of arms and draws it . Donna half - jokes with Greeves beside her , " Well , we know the butler didn ' t do it . " The Doctor asks in response , " Then who did ? " The Doctor rushes back in with the sword in hand and the others in tow , the lights come back on . The wasp is nowhere to be found . Lady Eddison , who was in her seat the whole time , then notices that her necklace , " the Firestone " , is stolen . Davenport then sadly says Roger ' s name . Robina looks over to Roger and reflexively screams in horror , but Lady Eddison ' s wails quickly drown her out . The Vespiform has stabbed Roger in the back , and he has slumped forward into the soup . Lady Eddison goes over to her son , crying over his death . Later , in the sitting room , the lightning and thunder continue outside . Agatha is trying her best to cope with what ' s happened , with the Doctor at her side . Donna enters , feeling sorry for Davenport ; he can ' t mourn Roger , because of the social mores of the 1920s . Agatha then asks Donna if she inquired about the Firestone . According to Donna , it ' s a priceless jewel that Lady Eddison brought back from India 40 years ago . The Doctor then begins wondering why the Vespiform hasn ' t used its abilities to kill them all already ; instead its been playing this game . Agatha tells the Doctor to stop as she knows the murderer is as human as them . The Doctor then realises that Agatha is right . He tells her that he ' s been so caught up in figuring out this giant wasp , that he ' s forgotten that " she ' s " the expert . Agatha again refuses to believe her work is any good , dismissing herself as " just a purveyor of nonsense " . The Doctor tells her that the reason her books are so good is because she knows the human mind well . If anyone can solve the case , it is Agatha . With her confidence restored , Agatha , the Doctor and Donna call the remaining four suspects together in the sitting room . The Doctor introduces Agatha , inviting her to begin . He takes a seat beside Donna . Between the two of them — the Doctor with his head rested on his hand and Donna munching a tray of grape s like one might eat popcorn — they both look ready for something big to unfold . Agatha starts with Robina and quickly exposes her as an impostor due to her terminology , saying " toilet " instead of the upper - class " loo " . They found the thief tool box below " her " bathroom window . Agatha concludes Robina must have thrown them out when she heard Donna was searching the rooms . " Robina " is the Unicorn ! Losing her fake posh accent for an East - End one , the Unicorn reveals she stole and still has the Firestone , handing it over to the Doctor . She tells them that although she may be a thief , she ' s no killer . Agatha then turns her attention to the Colonel . He confesses that he does not actually need his wheelchair . He faked a disability in order to keep Lady Eddison at his side , fearing she would fall in love with another man , to which she is quite touched . When asked how Agatha figured out the truth , she tells him that she didn ' t . Much to his embarrassment , she was simply going to say he was innocent . Agatha picks up the Firestone and says that it has quite the history — and is far more than the Unicorn ' s prize . She turns to Lady Eddison , who quickly pleads her innocence . Agatha asks Lady Eddison to tell them the story of bringing the jewel back from India , then suffering from malaria and keeping herself confined in her room for six months . Then , ignoring her pleas to stop , Agatha concludes that Lady Eddison actually came back from India pregnant . She concealed it with the aid of Miss Chandrakala , her Indian maid and confidante who would eventually become her housekeeper . Colonel Curbishley asks his wife if it ' s true ; she confesses it is , explaining she had no choice but to hide her pregnancy because of the scandal and shame it would bring to the family name . After all , " I ' m British . . . I carry on . " ; Lady Eddison then drinks some liquor to calm her nerves . The Doctor then takes control from Agatha momentarily , as they are now in " his " territory ; he states that it was no ordinary pregnancy Lady Eddison experienced . The one thing about the dining room murder that has left him puzzled is her exclaiming " It can ' t be " at the sound of the Vespiform ' s buzzing ; Lady Eddison tells the Doctor that he would never believe her if she told him . However , Agatha encourages Lady Eddison by explaining that the Doctor has opened her own mind into believing in the many possibilities the universe can hold . Lady Eddison explains . In 1885 , she was alone one night in Delhi , when she saw a purple shooting star land nearby . The next day , she met a young man named Christopher , with whom she quickly fell in love and had an affair . Christopher revealed that he was a Vespiform who took human form to study Earth , but Lady Eddison loved him so much , she didn ' t care . Soon after , during the great monsoon when the Jamuna River broke its banks , he drowned . However , he left her both the Firestone and pregnant . Out of shame of the scandal that her out - of - wedlock baby would bring , Lady Eddison sadly gave up the child for adoption . Donna then realises that " maiden " on the paper meant " maiden name " , which Agatha verifies as the reason Professor Peach was killed . He had found out who the child was and who his parents were , by discovering the birth certificate . Agatha then tells Lady Eddison that Miss Chandrakala had ( correctly ) feared that Professor Peach had found out the truth . She was coming to warn her . Just as Lady Eddison is about to break down , Agatha says that she is " innocent " of murder . She turns it back over to the Doctor . He pops up as Agatha sits back down and starts , " Thank you ! At this point , when we consider the lies and the secrets that are key to these events . . . " Firstly , the Doctor points at a confused Donna . However , he simply says that she was right — the vital clue was that everything in this story has been acted out like a murder mystery . He next points at Agatha . Donna wonders if Agatha was involved , as Agatha is taken aback . The Doctor dismisses the idea quickly , saying that she simply wrote those brilliant , clever books . The Doctor then points at Lady Eddison , who is such an admirer of Agatha ' s works , and asks what she was doing the previous Thursday night . It turns out that Lady Eddison was reading her favourite Agatha Christie book ( " The Murder of Roger Ackroyd " ) . She asks how it is relevant . The Doctor then points out that the church robbery which Golightly foiled also happened on Thursday night . He goes on to point out how unlikely it would have been for Golightly to defeat two strong , younger men . It has also been forty years since Lady Eddison gave birth . . . and Golightly is 40 years old . Lady Eddison is stunned as the Doctor proclaims , " Your child has come home . " He recalls Golightly ' s earlier statement that he was taught by the Christian Fathers , meaning that he was raised in an orphanage . The Doctor postulates that the night of the robbery , Golightly became deeply angry for the first time in his life . The genetic lock keeping him in human form was broken , and his alien biology was awakened . He transformed , frightening the thieves into submission . The Doctor then takes the Firestone and holds it up , revealing that it is actually a Vespiform telepathic recorder . It is part of Golightly ' s brain and his very essence . When Golightly transformed for the first time , the Firestone also activated and beamed his full identity directly into his mind . Because Lady Eddison was both wearing the Firestone and reading a book by Agatha at the time , his template for how the world should work was distorted - to him , it was an Agatha Christie murder mystery . After all the false starts , Donna wonders if Golightly is definitely the murderer ; the Doctor confirms it . Slightly miffed , Golightly says the evening has been entertaining and asks Lady Eddison if she believes what she ' s heard - but buzzes on saying her name . He does it again when the Doctor asks him to repeat what he just said , before warning the Doctor not to make him angry . Golightly sneers at the others , saying that humans worship tribal " sky gods " while he is so much more . After the upload of information from the Firestone , he wanted to take what was his , inheriting the Eddison title . Blinded by rage , Golightly focuses on Agatha Christie , asking why he shouldn ' t just kill everyone , as a pink light surrounds him . Completely losing his temper , Golightly transforms into his wasp form . A frantic Lady Eddison reaches out as if to hug him , but is held back by the others as they retreat into a corner . At this Agatha snatches the Firestone , screaming , " No ! No more murder ! If my imagination made you kill , then my imagination will find a way to stop you , foul creature ! " As she runs out of the room with Lady Eddison still screaming hysterically , Golightly pursues her and the Firestone , with the Doctor and Donna following them . Agatha takes a car and drives away , yelling for Golightly to chase her , which he does . The Doctor and Donna follow the two of them in the late Professor Peach ' s car . The Doctor ominously warns that " time is in flux " - history may change , and it may be that tonight could be the night that Agatha Christie loses her life ! Agatha leads the creature to the Silent Pool lake . Stopping , she gets out and calls Golightly to her . As they arrive and hurry to her side , Donna realises that Agatha is controlling Golightly . The Doctor notes that Agatha is linked to his mind because his mind is based on her thought processes ; Agatha replies that if she dies , then it might die with her . The Doctor tries to persuade Golightly that he was not meant to be a killer , and has the wrong template in his mind . Donna seizes the opportunity to snatch the Firestone from Agatha ' s grasp and hurl it into the water . Golightly shoots over their heads , splashes into the lake and is drowned , as his father had been in the Indian monsoons forty years before . A purplish light emanates from the spot where the Firestone and Golightly sank . Agatha gives a poetic speech as the purple light fades in the water — " Death comes as the end and justice is served . " The Doctor decides to call this adventure " Murder at the Vicar ' s Rage " ; at a look from Donna , he admits that the title needs some work . Agatha tells the Doctor there is just one more mystery left : who is he ? However , she then cries out in pain and collapses . As the Doctor catches her , he realises that the two are still linked . If the Vespiform dies , so does Agatha . . . However , Golightly cuts the link right before he dies . Agatha is bathed in the purple light for a few moments before she merely exhales deeply and faints . The Doctor remarks that it let her go . . . At the end , it chose to save her life . Donna then wonders what will happen now as the Doctor finally figures out how Agatha lost her memory . It was caused by the psychic trauma of the link between her and Golightly being severed so violently . Donna is sad that this means she ' ll forget meeting them . The Doctor says that they ' ve solved their mystery and can now let — or help — history take its course . Keeping with the established timeline , the Doctor leaves Agatha ' s car by the lakeside , takes Agatha in the TARDIS and drops her off at the Harrogate Hotel ten days later . As they watch a confused Agatha wander over to the hotel , Donna wonders about Lady Eddison , the Colonel and the servants , asking if they would tell anyone about what happened . The Doctor reminds her that they are far too " British " to tell such a shameful story , and that the Unicorn would have escaped back to London . Donna then wonders what will become of Agatha ; the Doctor explains that she will get married again , see the world and keep writing . Donna sadly tells the Doctor that Agatha never thought her work was any good as they board the TARDIS . In the TARDIS , the Doctor tells Donna that he thinks Agatha never " quite " forgot what happened as he pulls open a hatch below the TARDIS floor . He pulls out a chest , where he stores souvenirs under the letter " C " . Amongst the various knick - knacks he tosses out of it ( including the globe imprisoning the Carrionite s and the chest emblem from a Cyberman ) , the Doctor produces " Death in the Clouds " , an Agatha Christie novel which features a gigantic wasp on the cover . Donna is shocked . The Doctor points out that as she had such a great mind that some of the details bled through — stuff her imagination could use , such as the character of Miss Marple and the basic plot for " Murder on the Orient Express " . However , the Doctor then has Donna look at the copyright page in front , which shows that the book is a reprint from the year five billion . Agatha Christie is quite literally the most popular writer of all time . Donna then reminds the Doctor that Agatha never thought her work was good , but the Doctor responds , " Well , no one knows how they ' re going to be remembered . All we can do is hope for the best . Maybe that ' s what kept her writing . Same thing keeps me travelling . Onwards ? " He asks Donna with a smile . " Onwards , " she says , returning the smile . He pulls a lever on the console and they set off .