Logopolis

Logopolis is the seventh and final serial of the 18th season in the British science fiction television series Doctor Who, which was first broadcast in four weekly parts from 28 February to 21 March 1981. It was Tom Baker's last story as the Fourth Doctor and marks the first appearance of Peter Davison as the Fifth Doctor. This serial also marks the first appearance of Janet Fielding as new companion Tegan Jovanka, whilst Nyssa, played by Sarah Sutton and seen in previous serial The Keeper of Traken,^[2] returns and also joins the Doctor as a companion.

Warned of upcoming danger by the TARDIS' Cloister Bell, the Doctor decides to stay out of trouble, and instead spends time fixing his broken chameleon circuit by extracting the measurements of a true police box on Earth in order to give to the mathematicians of the planet Logopolis. He is unaware that the Master is aware of his plan, and materialises his own TARDIS in a recursive loop with the Doctor's. The Doctor and Adric work out the recursion, and attempt to flush the Master out by materialising the TARDIS in the River Thames, but instead land on a boat on the river with no sign of the Master's TARDIS. Outside, the Doctor sees a glowing white figure, the Watcher, who directs him to hurry to Logopolis. In flight, they discover they have picked up a passenger, Tegan Jovanka, an airline stewardess who wandered into the TARDIS to call for help to fix her aunt's flat tyre; the Doctor informs her the Master has killed her aunt with his Tissue Compression Eliminator.

On Logopolis, where the mathematicians perform their block-transfer calculations by chant-like verbal communication, the Doctor gives the lead mathematician, the Monitor, the new dimensions for the TARDIS. Discovering the calculation result to be flawed, the Doctor discovers the Master's handiwork in the death of several mathematicians. Returning to the Monitor, the Doctor finds the Master, who through mind-control of Nyssa (who believes him to be her father) is holding the Monitor hostage. The Master demands to know the secret behind Logopolis' science and the purpose of an exact replica of a space telescope from the Pharos Project on Earth, using a device to temporarily silence the mathematicians. The Monitor is horrified to find that even when the Master disables the device, the mathematicians have gone silent, and they discover that Logopolis is being overrun by entropy and turning to dust. The Monitor reveals that their calculations were used to model Charged Vacuum Emboitments (CVEs) as a means of excising off excess entropy from this universe into others as to stave off the imminent heat death of the universe; without the calculations, the CVEs have disappeared. Before the Monitor turns to dust, he reveals that a program contained in the bubble memory of their computers may be able to restore one CVE. The Doctor and Master agree to work together to return to Earth and use the Pharos Project there. Meanwhile, Nyssa, after having been freed of the Master's control and Adric are abducted aboard the Doctor's TARDIS by the Watcher and taken far outside of the galaxy, where they observe a large section of the universe including the Traken Union consumed by entropy. They manage to reset the controls for Earth, locking in on the Master's TARDIS when it arrives.

While the Doctor's companions set to distract the guards, the Doctor and Master make their way to the control room and successfully execute the CVE program. However, the Master reveals he plans to hold the universe hostage, threatening to stop the program. The Doctor is forced to climb onto the telescope's dish and disconnect a power cable while the Master attempts to turn it to knock the Doctor off. While the Doctor is successful in ending the Master's threat, he hangs precariously from the dish and sees images of his various enemies before he falls to the ground. The Doctor's companions rush to the spot where he has fallen. Dying, the Doctor experiences visions of the companions that have accompanied his current form and observes, "It's the end... but the moment has been prepared for." They turn to see the Watcher approach, and as he does so he merges with the Doctor. Nyssa realises that the Watcher was the Doctor all the time. As the companions look on, the Fourth Doctor regenerates into a new, younger body – the Fifth Doctor.

This story continues a loose arc of three serials featuring the Master. The trilogy began with The Keeper of Traken (1981) and concludes in Castrovalva (1982). Although the Master does not appear until Part Three, his laughter can be heard in the first two episodes and Anthony Ainley is credited accordingly. The story also concludes a long thread over the preceding season, discussing entropy. In particular, Logopolis serves as punctuation to the overarching events of the earlier "E-Space Trilogy". Several elements of this story carry over into Castrovalva, such as the theme of recursion.

The Doctor and Adric look at Romana's now deserted room in the TARDIS and talk about her recent departure in Warriors' Gate. The Doctor eventually jettisons her room to escape the pull of the Master's TARDIS. Before the Doctor falls from the dish, the enemies that mock him are the Master (as seen in The Deadly Assassin), a Dalek (Destiny of the Daleks), the Pirate Captain (The Pirate Planet), the Cyberleader (Revenge of the Cybermen), Davros (Genesis of the Daleks), a Sontaran (The Invasion of Time), a Zygon (Terror of the Zygons) and the Black Guardian (The Armageddon Factor). After falling, as the Doctor lies sprawled on the ground, he sees visions of all the companions that previously accompanied his fourth incarnation: Sarah Jane Smith (Terror of the Zygons), Harry Sullivan (The Sontaran Experiment), Brigadier Lethbridge-Stewart (Invasion of the Dinosaurs, a Third Doctor story), Leela (The Robots of Death), K-9 (The Armageddon Factor), Romana I (The Stones of Blood) and Romana II (Full Circle).

As pointed out in About Time 5, by Lawrence Miles and Tat Wood, this serial has arguably the largest number of deaths of any Doctor Who story—albeit mostly off-camera, as the destruction of Logopolis apparently causes a significant portion of the entire universe to be swallowed by a wave of entropy. At the very least, the Traken Union is destroyed, which would put the death toll in the billions and making the Master a mass murderer of unprecedented proportions, albeit one caused incidentally.

The spin-off BBC Books novel The Quantum Archangel by Craig Hinton briefly shows an alternate timeline where the destruction of Logopolis did result in the death of the universe. The Doctor Who Unbound audio play He Jests at Scars... depicts a timeline in which the Valeyard attempts to undo the events of this story by destroying Logopolis before the Fourth Doctor visited it.

This story features the Doctor's TARDIS materialising around the Master's TARDIS,^[3] something which occurred once before in The Time Monster. The Master suggests that the Time Lords will not approve of the Doctor's alliance with him and will cut all ties to him, yet this is never mentioned in any of the Doctor's later dealings with them. The DVD information text suggests that this is Christopher Bidmead's attempt to write the Time Lords (and the series' increasingly complex backstory) out of the series altogether, but it was never carried through in later series.

The projection of the Doctor's future incarnation (in the form of the Watcher) is similar to the future projection of his mentor K’anpo Rinpoche (in the form of Cho-Je) in the Doctor's previous regeneration story, Planet of the Spiders. A similar Watcher is present in the Fifth Doctor's mindscape in the Winter segment of the Big Finish audio play, Circular Time.

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The location scenes at the Pharos Project were filmed at a BBC receiving station in Crowsley Park, with a model standing in for the radio telescope and not the Lovell Telescope at the Jodrell Bank Observatory. The lay-by seen at the start was filmed on the southbound side of the A413 Amersham Road, Denham near Gerrards Cross. The lay-by is still there but the M25 now bridges the road where the scene was filmed.

The closing titles sequence was recompiled with Tom Baker's face removed from the closing credits of Episode 4, and with Peter Davison's face added for the following story, Castrovalva. Episode 4 of this story was the last time, for the next 24 years, the lead character was listed in the credits as "Doctor Who" (thus making it the only time Peter Davison was credited as "Doctor Who"). Beginning with the next story, Castrovalva, until the series' cancellation in 1989, the character was credited simply as "The Doctor". The 1996 television film did not have an on-screen credit for the Eighth Doctor, but listed the Seventh as the "Old Doctor". The 2005 relaunch returned the credit to "Doctor Who", and then again to "The Doctor" in "The Christmas Invasion" (at the request of David Tennant). Also, Episode 4 was the first to credit two actors as "Doctor Who" or "The Doctor" when a regeneration scene was involved. It also happened at the end of Episode 4 of The Caves of Androzani. In both instances, Peter Davison was billed second.

According to Christopher Bidmead, the Logopolitans employ a hexadecimal, or base-16, numerical system, a real system commonly used in computer programming. When Adric and the Monitor read strings of numbers and letters, the letters are actually the numbers between 10 and 15, expressed as single digits.

The Police Box that the Doctor materialises the TARDIS around in Part One was intended to be the one located at the Barnet bypass, which at the time was one of the last police boxes in the Metropolitan Police District still in its original location, though it had ceased functioning in the 1970s. It was removed in 1981 prior to the filming of this story.

Logopolis was repeated on BBC2 in November/December 1981, as part of "The Five Faces of Doctor Who".

Template:Infobox Doctor Who book A novelisation of this serial, written by Christopher H. Bidmead, was published by Target Books in October 1982. An unabridged reading of the novelisation by Bidmead was released by BBC Audiobooks in February 2010, with a completely new cover.

The story was released on VHS in March 1992. In January 2007, the serial was released on DVD as part of a trilogy, entitled New Beginnings, alongside The Keeper of Traken and Castrovalva. Logopolis was also released as part of Issue 46 of the Doctor Who DVD Files, published 6 October 2010.

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• Logopolis at BBC Online
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• On Target — Logopolis