The Lazarus Experiment ( TV story ) The Lazarus Experiment was the sixth episode of the third series of " Doctor Who " . It saw regular writer Mark Gatiss take on an acting role and marked the Doctor ' s acceptance of Martha as his regular companion . It included a large number of " " references and saw Francine Jones ' first involvement with his aides . It once more brought up the Doctor ' s perspective on a long life ; in his eyes , a long life only ensures one will end up alone as everyone and everything else turns to dust . Synopsis . To have an adventure investigating the unusual , there ' s no time like the present ! After travelling backwards , forwards and backwards again in time , Martha Jones has returned home . However , before the Tenth Doctor can bid farewell to her , he hears Professor Richard Lazarus announcing that he ' ll " change what it means to be human . " What could this mean ? And could it lead to something far more dangerous than a simple scientific failure ? Plot . The TARDIS materialises in Martha ' s flat . The Tenth Doctor tells her that they had agreed — one trip and home . It is about twelve hours after they left , something the Doctor failed to do with Rose in his previous life . Martha ' s phone rings , but she does not pick it up ; it is her mother Francine , saying that her sister Tish is on the news . Martha turns the television on and , alongside Tish , an elderly man , Professor Richard Lazarus , announces that tonight he " will change what it means to be human . " Though looking thoroughly perturbed at what was just said , the Doctor says goodbye to Martha and , oblivious to her upset , steps into the TARDIS . It dematerialises , but quickly rematerialises . The Doctor reemerges , saying , " No , I ' m sorry , did he say he was going to change what it means to be human ? " . Evidently , he cannot resist this . At Lazarus Laboratories , Professor Lazarus and Lady Thaw discuss the need for the experiment to work , with Thaw mentioning that is funding their research . Tish comes in , asking if Lazarus would like to check over the guest list again . He stops her and tries flirting by asking what kind of perfume she wears ; she tells him " soap " and quickly excuses herself . The Doctor and Martha attend Professor Lazarus ' black - tie reception that evening , where the Doctor complains about how something bad always happens when he wears black tie . Martha remarks that it is simply him , not the outfit , and that she thinks it makes him look like James Bond in a way , flattering him . There , they meet Martha ' s mother and her brother Leo . Martha introduces the Doctor to her family ; Francine is suspicious of him . Tish also meets the Doctor , wondering how he got in as he ' s not on the guest list . Martha explains Tish works in the PR department before Tish corrects her ; she ' s " head " of the PR department , having put together the party herself . The Doctor inquires what kind of experiment Lazarus is going to perform with the large capsule in the room , being labelled a " science geek " by using big words . He questions Martha as to what it means , seeming rather pleased with the answer . The lights of the room dim and a spotlight focuses on Lazarus , who announces he is to perform a " miracle " , which will outstrip all other human accomplishments in the field of science , even the splitting of the atom and the landing of Armstrong on the Moon . Declaring that they will wake tomorrow to a world changed forever , the elderly professor steps into the manipulator ' s capsule . Technicians flip the switch and the capsule flares to life with a blinding flash of light ; four manipulator arms circle the capsule at breakneck speed while manipulating threads o light up and down it . As the machine builds in intensity , an alarm blares and the consoles smoke and spark . The Doctor notices that the system is overloading and jumps in to avert disaster . Lady Thaw demands that someone stop him , but the Doctor declares that if the machine explodes it will take the entire building with it . He pulls the plug , and the machine comes to a stop . Martha rushes forward at the Doctor ' s urging and yanks the door open . The crowd advance slowly on the capsule . Out of the steam steps a young blond man ; Lazarus . He smiles as he touches his newly rejuvenated face and declares that he is 76 years old " And I am reborn ! " . Despite the momentary crisis , his experiment appears to have been a success — but the Doctor is certain there are dangers the professor has overlooked . He talks to Lazarus about having experience with a similar process , taking notice that he ' s experiencing hunger from a depletion of energy ; the Doctor tells him that he couldn ' t have thought of " all " the variables that could have happened . Lazarus arrogantly scoffs at the Doctor ' s warnings , so the Doctor and Martha sneak off to conduct their own tests , taking a DNA sample from Martha ' s hand , which Lazarus has just kissed . Their test shows Lazarus ' s DNA suddenly spike and change ; something which should be impossible . The Doctor reels off a lot of complicated scientific lingo but simplifies it for Martha ' s benefit . The esteemed professor hacked his own DNA and instructed it to rejuvenate . However , " something ' s been activated ; something that won ' t let him stabilise , something that ' s trying to change him . " Meanwhile , Lazarus speaks with Lady Thaw in his office on the top floor , telling a story about his childhood during World War II . Thaw expresses her desire to be the next to be rejuvenated so they can continue their partnership both personally and professionally . He rejects her , joking that not only did he learn cruelty from her , she has a gift for it . As she threatens to complain to Mr Saxon , Lazarus begins spasming . To Thaw ' s horror , Lazarus mutates into something horrendous . A scorpion - like tail raises itself and lunges at her . Downstairs , Francine asks Tish and Leo whether Martha has ever mentioned the Doctor to them before . She worries there is " something going on " , but Leo tries calming her down by saying Martha ' s found someone to be with . Lazarus returns to the reception , back to being himself and wearing a different suit , and invites Tish upstairs with him . Tish , now willing to return his advances , follows without argument . The Doctor and Martha emerge in Lazarus ' office , searching for him . As Martha suggests trying back at the reception , her voice trails off as she spots a bony leg sticking out from behind the desk . Investigating , they find the shriveled husk of Lady Thaw ; the Doctor says she had all the life energy drained to supply energy to the processes caused by Lazarus ' fluctuating DNA . Worried he will kill again , they go back downstairs , only to learn that he has gone off with Tish . They rush off , the Doctor accidentally spilling a drink on Francine . Another man replaces her drink , and darkly warns that Martha should be more careful in choosing her friends . Lazarus takes Tish to the roof , where he talks about nearby Southwark Cathedral and quotes T . S . Eliot , a quote the Doctor completes before they trade barbs ; Lazarus believes he has perfected humanity by purging it of mortality , while the Doctor is infuriated at his disregard for the laws of Nature . As they argue , Martha gets Tish away from Lazarus before he transforms . They stand , transfixed in horror , as they behold Lazarus ' mutated form ; resembling a huge , skeletal scorpion , a facsimile of Lazarus ' face stares out of the monstrosity . They flee indoors and the Doctor seals the door behind him . As they wait for the lift , Lazarus ' attempts to smash the door down triggers a security lockdown ; the lights dim , the lifts stop and the exits seal themselves , much to the confusion and slight panic of the guests . Rushing downstairs , the Doctor gives Martha the sonic screwdriver to unlock the doors , and warns everyone at the reception to get out . One woman refuses to believe this , stating jokingly that the biggest danger is choking on an olive . Suddenly , all heads turn as a great shattering of glass is heard and Lazarus appears on a balcony overlooking the reception area , roaring loudly . Now more inclined to listen , the assembled guests scream and scatter as Lazarus wreaks havoc , striking Leo in the head with a table . As Martha finally gets the doors open and the partygoers scramble down the stairs , Lazarus advances on the olive woman and deploys his stinger ; the Doctor shouts for him to leave her alone , but too late . Guests still in the room avert their eyes as the woman ' s withered husk hits the floor and Lazarus turns towards a prone Francine and Leo . The Doctor draws Lazarus away from Francine by taunting him that Nature has gotten her revenge for his defiance . Lazarus chases the Doctor down a corridor . Martha examines Leo , gets everyone out of the building , and goes back inside to help the Doctor despite Francine ' s protests . Tish guesses that " maybe she loves him " . The man who replaced Francine ' s drink earlier calls the Doctor " dangerous " , and whispers in Francine ' s ear the things he says she " should know " about him . The Doctor turns on the gas in a lab and leaps away from the resulting fireball , but Lazarus survives . Martha hears the explosion and finds the Doctor as she runs toward its source . She returns the sonic screwdriver to the Doctor . They flee together , and end up hiding in the capsule of Lazarus ' machine , on the Doctor ' s hunch that Lazarus is unlikely to destroy his own creation even to get at them . The Doctor starts fiddling about with the wiring inside as the Lazarus creature futilely searches for a way in . Martha , still unsure of where it came from , inquires if it is alien but the Doctor nixes that ; for once , the horrible creature trying to kill them is strictly human in origin . Martha reacts with disbelief , as the creature couldn ' t look any less human , but the Doctor explains that what happened is the machine unlocked something hidden away in Lazarus ' gene s ; an option which evolution rejected for humanity , but the potential for which still lies dormant . Martha likens it to Pandora ' s Box , but their ruminations are cut short as Lazarus switches the machine on . The Doctor " reverses the polarity " so that the capsule will reflect the energy rather than receive it , which it does explosively . The shockwave blasts the creature away , transforming Lazarus back to human in appearance — and apparently killing him . As they gaze upon the body , Martha and the Doctor reflect on how pitiful he looks , the latter quoting T . S . Eliot : " This is the way the world ends , not with a bang but a whimper . " Outside , as the ambulance carrying Lazarus ' body pulls away , Francine slaps the Doctor , and tells him to keep away from Martha . Suddenly , all turn their heads when they hear a loud crash nearby . The Doctor , Martha and Tish take off and find that the ambulance has gone off the road . Opening up the back doors , they find that Lazarus has killed both paramedics for their energy and escaped . They find him in human form inside Southwark Cathedral , where as a child he took refuge during the London Blitz . The Doctor says he was present during the Blitz , but Lazarus says that he is not old enough to have been there . They argue again about the benefits and curse of longevity . Martha ( accompanied by Tish ) then lures Lazarus away to the top of the bell tower ; the Doctor told her earlier that Lazarus could be defeated if he could just get him up there . As the Lazarus monster chases the Jones sisters at the top of the cathedral , the Doctor pulls out all the stops on the pipe organ , inserts the sonic screwdriver , and plays it at maximum volume , setting up a resonance in the bell above Lazarus that interferes with his sonic - based experiment . Lazarus falls to the cathedral floor below , transforming one last time — back into the elderly man he once was . Back in Martha ' s flat , the Doctor offers Martha one more trip , but Martha refuses to go with him on that basis , as a mere passenger being given a treat . The Doctor says , " Okay , then , if that ' s what you want . " She thinks he means to leave her again , but he indicates with a nod that she is welcome to rejoin him on her terms , and admits she was " never really just a passenger " . They leave together in the TARDIS . As it disappears , Martha ' s phone rings ; it is Francine . She warns Martha about " who this Doctor really is " , saying , " This information comes from Harold Saxon himself . You ' re not safe ! "