The Twin Dilemma ( TV story ) The Twin Dilemma was the seventh and final story of Season 21 of " Doctor Who " . It was the first full story to feature Colin Baker as the Sixth Doctor . It was also the last story to feature half - hour episodes until Season 23 , and the first episode since 1966 ' s " The Power of the Daleks " to feature a new Doctor ' s full debut partway through a season ( rather than at the start ) . The debut serial of the Sixth Doctor introduced a new and more colourful rendition of the starfield - themed title sequence by Sid Sutton , which featured the Sixth ' s Doctor ' s face appearing in a flash of rainbow streaks and changing from a smile to a large grin ( the first time a Doctor ' s face was shown to change facial expressions during the title sequence ) , as well as a slightly redesigned version of the show ' s neon tube - stylised logo , now more curved in an upward arc and with the addition of blue , indigo and purple highlights . Both the new title sequence and logo remained in use to the end of Season 23 . This story has received an especially bad track record for criticism . Three polls in 1998 , 2009 , and 2014 voted it the worst " Doctor Who " television story ever . ( DWM 265 , DWM 413 , DWM 474 ) The poll in 2003 used a different voting system and " The Twin Dilemma " was not among the twenty - five stories which received no votes , placing it higher than last place . ( DWMSE 6 ) Synopsis . A race of giant Gastropod s has taken over the planet Jaconda . Their leader , Mestor , now intends to cause an enormous explosion in order to spread his people ' s egg s throughout the galaxy , and he kidnaps juvenile twin geniuses from Earth to work out the necessary mathematical equations . Space fighters led by Lieutenant Hugo Lang are dispatched to get the twins back , but they come under attack and Lang is the sole survivor when his ship crashes on the asteroid Titan III . A newly regenerated Doctor and Peri become involved and help Jaconda ' s elderly former ruler Professor Edgeworth , who is really a Time Lord named Azmael , to defeat Mestor and free the planet ' s bird - like indigenous people from the gastropods ' reign of terror . Azmael , however , sacrifices his life in the process . Plot . Part one . After his regeneration following the events on Androzani Major and Minor ( TV : " The Caves of Androzani " ) , the new Doctor starts behaving erratically . Peri is still shocked by the Doctor ' s change and has him look at his reflection in her compact mirror . The Doctor is happy with his new features , and claiming not to be happy with his last incarnation and decides that he must change out of his predecessor ' s clothing and find a new outfit fitting his new persona . He goes to the wardrobe and starts looking for a new outfit , finding a glaring , mismatched , brightly coloured coat , to which he immediately takes a shine . Peri tells him that he could not possibly go outside wearing such an awful garb , to which the Doctor takes offence . Two twins , Romulus and Remus Sylvest , receive a visitation from a mysterious old man called Professor Edgeworth . They question how he managed to get inside their house . He tells them he will return when their father is there , then proceeds to take control of their minds . The trio disappear . They arrive on a spacecraft in deep space . Edgeworth then communicates with his superior , a slug - like creature called Mestor , who instructs Edgeworth to take the twins to Titan III . In the console room , the Doctor is working at the console after dressing in a terribly mismatched outfit . Peri enters in a new blue outfit similar to her old one and asks how it looks . The Doctor responds , " Yuck " , to her as she had done to his choice in clothing . He then quotes a poem about a peri — a good and beautiful fairy in Persian mythology , but one which used to be evil . The Doctor then accuses Peri of being evil , and of being an alien spy , before rushing toward her and throttling her . He catches a sight of his own manic face in a mirror and collapses in a heap , releasing Peri . When she tells him that he tried to kill her , he initially denies he could be capable of such an act unless it is in self - defence . Seeing how terrified of him she is , he decides he must become a hermit on the desolate asteroid Titan III as his punishment until he is properly humiliated . The twins ' father contacts the authorities ; he found Zanium in their room — a residue of their transmat and a sure sign of kidnap . Lieutenant Lang begins the pursuit and soon finds a suspicious ship previously reported missing . He tries to contact it , but it enters warp drive , something that class of ship is not designed to do . On Titan III , as the Doctor contemplates a thousand years of solitude and Peri expresses her disapproval , they hear the crash landing . Examining the wreckage , they find the concussed body of Lang . They take him back to the TARDIS where he reveals his whole squadron has been destroyed . Believing the Doctor to be responsible , he points his gun at the Time Lord and threatens to kill him . . . Part two . Peri pleads with Lang , telling him that the Doctor had in fact saved him , but he faints away . The Doctor is not keen to treat Lang , more concerned for his own life , but eventually agrees to Peri ' s persuasion . Edgeworth argues with Romulus and Remus , making them do Mestor ' s work . He scolds them for setting up a distress signal , so they are not allowed to use electronic equipment to solve the equations they have been set . An image of Mestor appears and gives the twins a more blunt threat — work for him or have their minds destroyed . On the TARDIS scanner , the Doctor and Peri see a building — something which has no place on an uninhabited asteroid . Leaving Lang behind , they find a tunnel which may lead to the building , but while exploring they are found two aliens wielding guns . The Doctor cowers in fear and pleads with them not to shoot him . They are led off and are brought before Edgeworth . The Doctor claims to be a pilgrim to Titan III , but Noma , one of the aliens , says they are spies and should be shot . The Doctor suddenly recognises Edgeworth as an old friend - Azmael , master of Jaconda , whom he last saw during his fourth incarnation . When the Doctor sees Romulus and Remus and discovers it is Azmael who has abducted them , he is disgusted . Azmael teleports away with the twins and the aliens , leaving the Doctor and Peri locked in the building . The Doctor starts to break the lock ' s combination , but Peri discovers Noma has set the base to self - destruct . The Doctor improvises a solution to teleport them back to the TARDIS . Peri makes a successful return , but the Doctor has not appeared when she sees the base explode on the scanner . . . Part three . A glimpse of the Doctor is seen appearing in the TARDIS ; he was delayed returning because he was using Peri ' s watch to synchronise their arrival , but the watch had stopped . The Doctor is surprised at Peri ' s compassion when she thought he had died . On Jaconda , Mestor is seen putting one of the bird - like Jacondan s to death for the petty offence of stealing a few vegetables . Soon , the TARDIS arrives , but instead of the expected beautiful planet the Doctor is expecting , he , Peri and Lang find a desolate wasteland covered with giant Gastropod trails . The Doctor is reluctant to go to the palace , scared for his own life , but is persuaded to take Lang there in the TARDIS . In the palace corridors , they see murals depicting Jaconda ' s history , depicting the slugs of myth - but it appears that they are now all too real . After avoiding some Gastropods , Lang gets stuck in their slime trail . Azmael takes the twins to his laboratory and shows them a store room full of Gastropod eggs . Mestor arrives and tries to persuade them that his aims are benevolent . Azmael begs him to stop reading his thoughts and stop Noma watching his every move . He agrees and leaves . Azmael explains to the twins that Mestor usurped him as leader of Jaconda and outlines a plan to draw two outlying planets into the same orbit as Jaconda . The twins ' genius is required to stabilise those planets in their new orbit . The Doctor , leaving Peri and Lang behind , finds Azmael ' s lab . In a manic fit of pique , he attacks Azmael , but is restrained by a Jacondan and the twins . The Doctor apologises to Azmael but demands to know what is going on . Meanwhile , Peri is captured by Jacondan guards and brought before Mestor . When Lang escapes to Azmael ' s lab and informs them what has happened , the Doctor finally shows compassion for her when he thinks she might die . . . Part four . Mestor refrains from killing Peri immediately , finding her appearance pleasing . Jacondan guards arrive in Azmael ' s lab and seize the Doctor . The Doctor tells Mestor that he ought to allow him to assist with the dangerous operation of moving the planets , as a single mistake could blow a hole in that corner of the universe . Back in the laboratory , Azmael informs the Doctor the details of the plan to bring the planets into the same orbit — they will be placed in different time zones using time travel technology that Mestor stole from Azmael . The Doctor realises that , as the other planets are smaller than Jaconda , bringing them closer to Jaconda ' s sun will lead to catastrophe . The Doctor enters the egg storeroom , and is disturbed that they have no nutritional mucus . He tries to cut one open with a laser cutter ; the shell is impenetrable , but the egg reacts slightly to the heat . The Doctor realises they have been designed to withstand the heat of an exploding sun — the explosion of the Jacondan sun will scatter the eggs throughout the universe . When they hatch , the Gastropods will conquer the universe . The one remaining Jacondan in the lab collapses dead , his mind burnt out . Mestor had been using him as a monitor , and knows the full details of what has been discussed . Peri , Lang and the twins return to the TARDIS , whilst the Doctor and Azmael go to confront Mestor . When Mestor refuses to abandon his plans , the Doctor hurls a vial of acid taken from the lab at him , but a force field protects Mestor from any harm . Mestor threatens to possess the Doctor ' s mind and body , and demonstrates by taking control of Azmael ' s body . Azmael tells the Doctor to destroy Mestor ' s body before he can return to it , which he does with a second vial . Then Azmael , in his last regeneration , forces himself to regenerate — killing himself — and in doing so destroys Mestor . Dying , Azmael says he has no regrets and that one of his fondest memories was a time spent with the Doctor by the fountain . The Doctor and Peri return to the TARDIS . Lang has no family back on Earth , and decides to stay behind on Jaconda to assist with their rebuilding . When Peri tells the Doctor off for being rude , he reminds her that he is an alien , with alien sensibilities : " I am the Doctor , whether you like it or not ! "