Archive Status: All four episodes exist as PAL 1” colour videotape, always held by the BBC’s Film and Videotape Library.

Colin Baker (The Doctor), Nicola Bryant (Peri Brown), Maurice Denham (Edgworth/Azmael), Kevin McNally (Hugo Lang), Edwin Richfield (Mestor), Gavin Conrad (Romulus), Andrew Conrad (Remus), Dennis Chinnery (Sylvest), Barry Stanton (Noma), Oliver Smith (Drak), Helen Blatch (Fabian), Dione Inman (Elena), Seymour Green (Chamberlain), Roger Nott (Prisoner), John Wilson (Jocondan Guard)

The Doctor's regeneration has left him mentally unstable. He changes his cricket attire for an outfit of clashing colours, including a multicoloured patchwork frock coat. After almost killing Peri during a fit of instability he decides to live as a hermit to avoid putting others at risk.

On Earth, mathematical genius twin brothers Romulus (Paul Conrad) and Remus (Andrew Conrad) are kidnapped by Professor Edgeworth (Maurice Denham). The kidnapping is discovered – tell-tale traces of a material called zanium are found on the floor – and a squadron of space fighters under the command of Lieutenant Hugo Lang (Kevin McNally) is sent to pursue the X.V.773 Space Hopper Mk III Freighter on which Edgeworth is escaping with the twins. The fighters are attacked, leaving Lang as the sole survivor when his ship crashes on the asteroid Titan 3. The TARDIS lands here too, and the Doctor and Peri find Lang in the wreckage. The Doctor reluctantly agrees to investigate a distant dome, which is in fact where Edgeworth has taken the twins as a halfway safe house on his journey back to the planet Joconda.

The Doctor and Peri arrive at the dome only to be captured by Edgeworth's two Jocondan guards, Noma (Barry Stanton) and Drak (Oliver Smith). Edgeworth is recognised by the Doctor as a retired Time Lord whose real name is Azmael. Azmael had ruled Joconda since his retirement, but the planet has now fallen under the control of a race of giant Gastropods – slug-like creatures from Jocondan mythology – led by Mestor (Edwin Richfield), who is now forcing Azmael to do his bidding.

The Doctor and Peri are left sealed in the dome as Azmael and the others leave for Joconda. When they are alone, they discover that the dome has been set to self-destruct – an action taken by Noma without Azmael's knowledge. The Doctor hastily adapts a Revitalising Modulator to transmit his and Peri's molecules back in time to the TARDIS and thus escape the destruction of the dome. To his amazement, it works.

Together with Lang, who had been left behind in the TARDIS to recuperate while they explored the asteroid, the Doctor and Peri journey to Joconda, where they are soon captured and imprisoned with Azmael. Mestor claims to need the twins' mathematical prowess to provide the energy equations required to realise his plan of placing the Jocondan sun's outer two planets into orbit around Joconda, thus providing a ready-made larder facility. To balance the gravitational forces, Mestor wants all three planets to occupy the same space, but in different time periods, one Jocondan day apart. The Doctor realises that as the outer planets are small, the gravitational differences will pull them into the sun and cause a massive explosion. This is Mestor's real plan, as the explosion will activate millions of his eggs and send them out into space to fall on to other worlds, thus populating the whole of space with the giant slugs.

The Doctor tries to destroy Mestor by throwing at him a vial of corrosive chemicals from Azmael's laboratory, but the attempt is thwarted when the creature raises a force shield around itself. Mestor now wants to possess the Doctor's body, and to prove that he is capable of doing so he attempts to mind-link with Azmael. While Mestor is distracted, the Doctor hurls a second vial of chemicals at him, and this time strikes the target. Azmael triggers his thirteenth and last regeneration, and Mestor's mind, having nowhere to flee now that his body has been destroyed, dissipates into nothingness. Unfortunately Azmael dies too. The threat from the Gastropods is lifted and the Doctor prepares to return the twins to Earth. Hugo elects to stay on Joconda to help the Jocondans rebuild their planet.

Synopsis from Doctor Who: The Sixth Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted.

Stephen Jeffery-Poulter (Assistant Floor Manager), Beth Millward (Assistant Floor Manager), Pat Godfrey (Costumes), Valerie Warrender (Designer), John Baker (Film Cameraman), John Walker (Film Cameraman), Ian McKendrick (Film Editor), Malcolm Clarke (Incidental Music), Denise Baron (Make-Up), John Nathan-Turner (Producer), Christine Fawcett (Production Assistant), June Collins (Production Associate), Eric Saward (Script Editor), Dick Mills (Special Sounds), Don Babbage (Studio Lighting), Scott Talbott (Studio Sound), Peter Howell (Theme Arrangement), Ron Grainer (Title Music), Stuart Brisdon (Visual Effects)

A very sketchy opening for the Sixth Doctor, with some electrifying scenes between Colin Baker and Nicola Bryant let down by an undeniably shoddy script and totally unengaging main story. A new opening and closing sequence -- much like the previous one but slightly "enhanced" -- debuts with this story. This was the first time a regeneration took place mid season since the Hartnell-Troughton change in 1966. The script was extensively rewritten by story editor Eric Saward. Among the clothing the Doctor looks for in the wardrobe are the fur coat worn by the second Doctor in "The Five Doctors," and a velvet jacket similar to the Pertwee incarnation. There is a musical cue for Tegan when the Doctor recalls her in part two. As had occurred many times before, production was affected by industrial action at the BBC; it eventually went into the studio about a month later than intended and, unusually, the location filming was done not in advance of but between the two blocks of studio work. Three Gastropod costumes were made for the story by Richard Gregory of the freelance effects firm Imagineering; the one for Mestor was more sophisticated than the other two, featuring an animated mouthpiece, and the mask was designed to be easily removable as the actor, Edwin Richfield, suffered from claustrophobia. Actor Paul Conrad's name was changed to Gavin due to Equity laws about actors sharing the same name. The cat badge worn by the Doctor in his lapel for this story was hand-made and painted by Suzie Trevor, and purchased for the programme from a specialist badge shop in central London. Fabian was originally envisaged as a male character, and the Jocondan Chamberlain as a female one.

Released as "The Twin Dilemma" in the UK [May 1992] and Australia/New Zealand [May 1993] (BBC catalog #4783), US/Canada [October 1993] (WHV catalog #E1101); episodic format, cover illustration Andrew Skilleter. Clips from this story, and from subsequent Colin Baker serials, are seen on "The Colin Baker Years," released in the UK [March 1994] and Australia/New Zealand [April 1994] (BBC catalog #5324), US/Canada [August 1994] (WHV catalog #E1267).

Novelised as "Doctor Who - The Twin Dilemma" by Eric Saward (Target #103), first released in 1985 with cover art by Andrew Skilleter. Rereleased in 1993 with cover art by Alister Pearson.

For more details on the various novelizations of this story, with additional background material, artwork and details of both UK and foreign releases, visit On Target.