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Logopolis was the seventh and final serial of season 18 of Doctor Who. It was the final regular appearance of Tom Baker as the Fourth Doctor and introduced Peter Davison in the role as the Fifth Doctor in the closing moments in part four. With this story ending Baker's 7 year tenue as the Doctor, this currently makes Baker, as of 2024, the longest serving actor in the role of the Doctor. It also introduced Janet Fielding as new companion Tegan Jovanka.

It also introduced an interim version of the Doctor known as the Watcher, whose sudden presence foreshadowed the regeneration of the Doctor. What triggered the Watcher's creation, however, was not fully explained, but writer Christopher H. Bidmead suggested that as multiple incarnations of the Doctor existed, it would be possible that a future, transitional version of himself could travel back in time to watch events unfold. (DOC: A New Body at Last)

After being introduced in the previous serial, Nyssa, played by Sarah Sutton, began her travels with the Doctor here. It additionally introduced a recurring element in the TARDIS's Cloister Bell. This was also Anthony Ainley's first full story as the Tremas Master.

On 13 March 2019 only, special cinema screenings of Logopolis were shown all around the U.S.A.[1]


The Doctor goes to Logopolis to repair the TARDIS' chameleon circuit, not knowing that a shadowy watcher is spying on him.

Meanwhile, his old enemy the Master has only recently gained secure longevity by possessing the body of Tremas, and revels in his safety. He has plans of his own for the planet of mathematicians, Logopolis, and a plan that could spell doom for the entire universe.

The Master's plan could rock Logopolis, the keystone of all life. Could this mean the unravelling of the causal nexus and the end of the universe itself?

The Doctor must pit his wits against the Master in a desperate battle to thwart his plans. But he is aware that this might be a fight which could easily spell the end of his life.


Part one[]

On the Barnet Bypass, a policeman is talking on the telephone of a police box in a lay-by. Suddenly, a TARDIS materialises around it in disguise and the phone goes dead. The TARDIS/police box door opens, the policeman is dragged struggling inside and there is an evil chuckle.

Meanwhile, the Fourth Doctor is pacing around the TARDIS Cloister Room, pondering decay and entropy. As he and Adric prepare to leave, the large bell in the centre of the room begins to ring. This worries the Doctor. The sound of the Cloister Bell is a sign of impending universal catastrophe.


The Doctor and Adric with the police box

To divert himself, the Doctor decides to repair the TARDIS' chameleon circuit, which has frozen it into the shape of a police box. To do this, he intends to materialise the TARDIS around a real police box, and then obtain its precise measurements in thirty-seven dimensions. With these measurements, he will have the inhabitants of the planet Logopolis produce a mathematical calculation — a Block Transfer Computation — to reset the circuit. However, the "police box" he materialises around is actually the TARDIS of the Master, who has survived their encounter on the planet Traken. When the Doctor materialises around the Master's TARDIS, a recursive loop of TARDISes within TARDISes is formed.

He's watching you

The Watcher - but what does he represent?

Meanwhile, an airline stewardess, Tegan Jovanka, is being driven to the airport by her Aunt Vanessa. The car gets a puncture and pulls onto the lay-by. Tegan decides to go to the "police box" to call for help, but finds herself lost in the TARDIS instead. The Doctor and Adric enter another police box in a duplicate TARDIS. The Doctor, telling Adric to wait behind, finds himself emerging from behind the police box. He meets uniformed police officers, led by a plain-clothes Detective Inspector, who have found the shrunken, dead bodies of Tegan's aunt and the other policeman in the car. The Doctor realises that the Master has escaped from Traken and must be somewhere nearby.

Part two[]

The police think the Doctor has caused the incident, but Adric creates a distraction with the policeman's bicycle he has found. This allows the Doctor to escape to the TARDIS, followed by Adric. In the distance, a mysterious, white-clad stranger watches the proceedings. The Doctor dematerialises the TARDIS, leaving behind the real police box. When the Detective Inspector uses the police box's key to open the door, he and his colleagues find only orange road warning lights inside. Realising that the shrunken bodies are the trademark of the Master, the Doctor decides to materialise the TARDIS underwater, to literally flush him out. The Doctor misses the River Thames, however, and lands on a small jetty instead. The mysterious stranger appears here too. He beckons to the Doctor, telling him to go to Logopolis.

As the TARDIS arrives on Logopolis, Tegan finds her way to the control room, annoyed. She asks where her aunt is. The Doctor, realising that Tegan's aunt was the dead woman in the car, evades the question. Once they exit the TARDIS, the Doctor asks the Logopolitan leader, the Monitor, for his help. The Logopolitans are able to model reality by pure mathematics and whatever they calculate can take physical form. Since block transfer computations cannot be calculated by machines or computers, the Logopolitans speak aloud a line of calculations and pass the results on.

Unknown to the group, the Master has arrived on Logopolis and killed several Logopolitans. Adric and Tegan meet with Nyssa, who says she was brought to Logopolis by "a friend of the Doctor". The Logopolitans' deaths have disrupted the calculations for the TARDIS. When the Logopolitans produce the requested computation, the Doctor tries it on the TARDIS. Before the eyes of Adric, Nyssa, Tegan and the Logopolitans, the TARDIS starts to shrink...

Part three[]


"Nothing like this has ever happened to me before...!"

The TARDIS is now half its normal size, but still shrinking. The Monitor has the Logopolitans carry the half-size TARDIS to the Central Registry where they can try to stabilise it. They use sonic projectors to produce a stasis field while the Monitor and Adric attempt to uncover the fault. (The Logopolitans use Earth numbers for their calculations, which the Doctor has taught Adric how to read.) Meanwhile, Nyssa identifies the Watcher, the mysterious white figure the Doctor spoke with, as the man who brought her from Traken. She is searching for her father. The Monitor and Adric work through the city and discover the shrunken bodies of three Logopolitans. Fixing the error this has caused, they bring the new computation to the TARDIS. Tegan holds the notes up to the TARDIS so the Doctor can read them via the scanner and correct the fault. The Doctor emerges from the restored TARDIS and tells Tegan that her aunt was murdered by the Master. Meanwhile, Nyssa finds the Master, whom she believes is her father as he is inhabiting Tremas's body. "Tremas" gives her a bracelet; it is actually a device which will allow him to control her actions.

Logopolis title

Nyssa discovers the Master killed her father, Tremas

The Master attaches a device to the sonic projectors and sets up a counter-wave that brings silence to the Central Registry preventing the Registers from making their calculations. He goes to the Registry's control room (a replica of the Pharos Project on Earth, a radio telescope tasked to seek out signs of extraterrestrial life). He demands the Monitor tell him the true purpose of Logopolis. The Doctor arrives with Adric and Nyssa. Adric deactivates the Master's device, but Nyssa, who is controlled by the Master, attempts to throttle him. Tegan restores the device and the Master repeats his demand. The Monitor warns the Master that bringing Logopolis to a halt will cause universal disaster, but the Master replies that it is only a temporary effect. He attempts to demonstrate this assertion by deactivating the suppression device.

The silence persists and the calculations do not resume. They go outside, and find all the Logopolitans dead, crumbling to dust, and the city collapsing. The Master thinks this is a trick and tries to have Nyssa strangle the Monitor, but the control device ceases to function. He tries to increase the device's power, but it falls apart as local decay increases. The Monitor explains the situation: the universe has long ago passed the point of heat death. To stave off final collapse, the Logopolitans have been modelling temporary Charged Vacuum Emboitments, like the one through which the TARDIS was previously transported into E-Space. The excess entropy generated by the universe had been passing through the CVEs to other universes. The Master's interference has closed the CVEs and the universe is now dying at last. The Doctor realises he has no choice. To save the universe, he has to work with the Master. He orders his companions into the TARDIS. When they argue about him working with the Master, the Doctor points out that he never chose to travel with any of them; Adric came aboard as a stowaway, Tegan's curiosity brought her into the Doctor's life, and Nyssa came to him asking for help to find her father. With that, the three return to the TARDIS. The Master holds out his hand to the Doctor on their agreement to work together. "One last hope," says the Doctor and they shake hands.

Part four[]

Adric, Nyssa and Tegan enter the TARDIS. The Doctor has the Watcher take it out of space/time. However, Tegan refuses to co-operate and follows the Doctor, the Master and the Monitor back to the Logopolis control room. The Monitor reveals that they had been completing a program to make the CVEs permanent. He prepares to use it on one of the surviving CVEs, but entropy takes hold of him. He disintegrates before their eyes. The Doctor dismantles the computer and realises the program is stored in bubble memory that they can use with the real Pharos Project. The Doctor, the Master and Tegan escape from Logopolis in the Master's TARDIS.

Adric and Nyssa watch helplessly in the Doctor's TARDIS as a portion of the universe is wiped out by encroaching entropy — including Traken. On Earth, the two Time Lords reconfigure the Logopolitan program and feed it into the Project's computers, but the Master points out that the transmitter is pointed away from the last surviving CVE. After speaking with the Watcher, Adric brings the Doctor's TARDIS to Earth as the Doctor and the Master run to realign the dish. The Doctor's companions distract the guards and the two Time Lords go to the dish's control room, hooking up a light speed overdrive from the Master's TARDIS to ensure the signal gets to the CVE in time. On transmission of the program, the CVE begins stabilising.

The Master's co-operation with the Doctor has been a ploy, however. Holding the Doctor at gunpoint with his Tissue Compression Eliminator, he transmits a message to the peoples of the universe, saying that if they do not acknowledge his rule, he will send a signal to close the CVE and restart the collapse. Realising that the Master has control of the CVE "only while that cable holds" the Doctor climbs onto the radio telescope's gantry to disconnect the power cable and the Master tries to prevent him by tilting the dish. The Doctor disconnects the cable, but falls off the tilted gantry. As he hangs onto the disconnected cable, visions of old enemies mock him: the decaying Master, a Dalek, the Captain, the Cyber-Leader, Davros, a Sontaran, a Zygon and the Black Guardian. Losing his grip, the Doctor plummets to the ground. The Master enters his own TARDIS, dematerialising before the Pharos Project guards reach the control room.


The fourth incarnation regenerates.

The Doctor's companions run to where he has fallen. Dying, the Doctor sees visions of the companions that have accompanied his current incarnation on his travels: Sarah Jane Smith, Harry Sullivan, Brigadier Alistair Gordon Lethbridge-Stewart, Leela, K9 and Romana's first and second incarnations. Smiling, he looks up at his companions who have gathered at his side and says, "It's the end... but the moment has been prepared for." They turn to see the Watcher approach, and Nyssa realises that "he was the Doctor all the time." As the companions look on, the Watcher merges with the dying Doctor, triggering his fourth regeneration. Moments later the Fifth Doctor sits up, beaming with a delighted grin.


Uncredited Cast[]



Astronomical objects[]

  • Traken and Mettula Orionsis (Traken's star) are mentioned, both of which Adric and Nyssa witness being destroyed by the entropy field spreading across the Universe.
  • The Doctor's transmission of the Logopolis program saves the rest of the Universe, starting with the constellation of Cassiopeia.

Cultural references from real world[]

  • The Doctor misquotes his "old friend Huxley" by saying, "“The cheese-board is the world; the pieces are the phenomena of the universe". He then corrects himself, says "chess-board" and continues to quote some more.
  • The Doctor mentions the second law of thermodynamics and entropy.

The Doctor[]


  • The Doctor has taught Adric how to read Earth characters. (This is confirmed by Adric reading the police box's instruction plate aloud in part one, and later telling the Monitor in part three that the Doctor taught him to how to read Earth numbers.)
  • The Master had temporarily taken the powers of the Keeper of Traken. This assisted him in possessing the body of Tremas.
  • The school uniform which Romana wore in Paris in 1979 ( TV: City of Death) is shown to be in her TARDIS bedroom.


  • The Doctor wants to materialise the TARDIS underwater, in the Thames, but the TARDIS lands on a small jetty near the banks.



  • The Doctor and Adric walk around the TARDIS cloisters.
  • The Cloister Bell is described as "a sort of communication device reserved for wild catastrophes and sudden calls to man the battle stations".
  • Just before the Master's TARDIS materialises into the Doctor's one, Adric and the Fourth Doctor guess a gravity bubble is responsible for the instrumentation failure of the TARDIS.
  • There are references to the TARDIS's faulty chameleon circuit and a demonstration of how it could function if properly working.
  • After picking up Adric and Nyssa, the Watcher disconnects "the entire co-ordinate sub-system" of the Doctor's TARDIS, which takes it "out of time and space".
  • The Master's TARDIS disguises itself as a police box, a tree and a Doric column at various times.
  • The Master suggests, "We reconfigure our two TARDISes into time cone inverters... We create a stable safe zone by applying temporal inversion isometry to as much of space/time as we can isolate.".
  • Through the Architectural Configuration, the Doctor jettisons Romana's room.


Story notes[]

  • The policeman using the telephone in the police box in the opening scene of the story is named in Christopher H. Bidmead's novelisation as P.C. Donald Seagrave. This was not derived from any information given in the televised version.
  • This serial arguably — as pointed out in About Time 5 by Lawrence Miles and Tat Wood — has the largest body count of any Doctor Who story, albeit not graphically shown, 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 make the Master a mass killer on an unprecedented scale, albeit not by intent. The Last Great Time War and The Flux potentially had a higher body count, but even were a death toll to be given, it occurred off-screen.
  • Christopher H. Bidmead's inspiration for the recursive loop scene came from the end of The Keeper of Traken, in which the Master escapes via a TARDIS within the Melkur, which was also a TARDIS. (DOC: A New Body at Last)
  • This story is the first to feature a human companion since Leela left the Doctor in The Invasion of Time, and the first to feature one from contemporary Earth since Sarah Jane Smith's departure in The Hand of Fear.
    • Coincidentally, both Elisabeth Sladen and Louise Jameson, who played Sarah Jane and Leela respectively, were asked to reprise their roles for Logopolis.[2]
  • The story was repeated on BBC2 on consecutive evenings from Monday 30 November to Thursday 3 December 1981 as part of the repeat season The Five Faces of Doctor Who. The Radio Times programme listing for the repeat of part one was accompanied by a black-and-white head-and-shoulders publicity shot of the Doctor taken during location filming for TV: The Masque of Mandragora, with the accompanying caption "Another trip through time and space for Doctor Who (Tom Baker): 5.40". (original published text)
  • Logopolis comes from two ancient Greek words and means "city of speech," alluding to the oral calculations recited by the Logopolitans.
  • This is the first regeneration story in which the Doctor is shown to be fully conscious immediately after regenerating, a precedent that would be followed by most later regenerations, with the sole exception of Time and the Rani (on account of the Sixth Doctor having already been unconscious as per the events of The Brink of Death).
  • The Doctor reveals a small panel on one of the TARDIS control panels, with a keyboard which the Doctor can input an exterior appearance for the TARDIS. This is the first instance that reveals the TARDIS's chameleon circuit can be manually overridden, so there is no need for the automatic system.
  • This is the last story for Barry Letts as executive producer and also the last story he contributed to.
  • Harry Andrews, Bernard Archard, Geoffrey Bayldon, Peter Cushing, Maurice Denham, Frank Finlay, Barry Foster, Marius Goring, Michael Gough, William Lucas, Nigel Stock, Frank Windsor and Peter Wyngarde were considered for the Monitor.
  • Alun Armstrong, Paul Jerricho, Alec Sabin, John Savident and Michael Sheard were considered for the Detective Inspector.
  • Dorothy Alison was considered for Aunt Vanessa. [1]
  • Either Sarah and/or Leela were considered to return in order to give a familiar face for the Fourth Doctor to go through his regeneration story and ensure a smooth transition. Elisabeth Sladen and Louise Jameson declined to return, so Nyssa and Tegan were brought in.
  • The Doctor was supposed to scream as he fell to his death. Tom Baker disagreed, as he felt it was unheroic. He was unhappy with the fact that the final image that viewers would see of his Doctor would be of him lying prone, being photographed from above.
  • It was decided to hold off the Master's first on-screen appearance until part three, in order to make the audience wonder if the Watcher might actually be the evil Time Lord.
  • During one take of the regeneration, Tom Baker turned to Matthew Waterhouse and said, "Adric, you're a c**t and you always will be".
  • Christopher H. Bidmead was a keen computer enthusiast, and used many ideas from computer science in developing his scripts, with elements such as the Monitor, block transfers, and registers all being derived from terminology in computer architecture. Eager to inject Doctor Who with real scientific notions, Bidmead also drew upon the physics discipline of thermodynamics, making heavy use of the concept of entropy: the measure of unavailable energy in a system, which effectively increases as a system becomes homogeneous. He got a lot of the ideas and language of the story from taking apart and looking at the inner workings of his Vector Graphics MZ system.
  • John Nathan-Turner noticed that a real police box still stood on the Barnet Bypass in London. Christopher H. Bidmead was fascinated with the TARDIS, and wanted to explore its properties more fully. The Barnet Bypass police box was the last of its kind left in the country. Sadly, the real police box was vandalised and demolished shortly before production started, so the TARDIS prop from the previous season was refurbished and used.
  • At the Longleat celebration, Tom Baker was asked why he left the series. He replied that he was pushed - by Anthony Ainley.
  • Christopher H. Bidmead defended the scenes where the Doctor attempts to flush the Master out of his TARDIS and the Master holding the universe to ransom with a tape recorder by asking "Does it seem far fetched now we have the internet?"
  • Tom Baker recalled on the DVD commentary that he was dreading leaving the series and was pretty angry all the time on the shoot. He couldn't take comments or direction from anyone. Janet Fielding confirms that he was angry with everybody. John Nathan-Turner claimed that when Baker had finished his last scene, he quietly slipped away without a word.
  • When the production crew was unable to locate the owner of the house that Peter Grimwade had originally intended to use for Aunt Vanessa's residence, they instead moved further up the same street to the home of Andrew McCulloch, who had co-written Meglos earlier that year.
  • Logopolis came from the Greek word for "city of numbers".
  • The Pharos Project was named for the Egyptian island on which once stood the Lighthouse of Alexandria, one of the Seven Wonders of the Ancient World.
  • The mystery surrounding the Watcher was felt to be a crucial element to hold the viewers' interest, and so it was decided to hold off the Master's first on-screen appearance until part three, in order to make the audience wonder if the Watcher might actually be the evil Time Lord in disguise.
  • Tom Baker started filming his final story three days after his wedding to Lalla Ward.
  • Filming had to proceed without Tom Baker and Matthew Waterhouse when a studio day for The Keeper of Traken was remounted after being cancelled by an industrial dispute by BBC electricians. As a result, the production crew focused on material involving Tegan at the lay-by on the Barnet Bypass.
  • This is the first story to return to the original 1963 companion lineup of one male companion, two female companions, since the departure of Ian and Barbara in The Chase. This would be the standard format for the majority of the next season as a deliberate throwback to the show's early years.

Closing credits[]

At the end of part four:


  • Part one - 7.1 million viewers
  • Part two - 7.7 million viewers
  • Part three - 5.8 million viewers
  • Part four - 6.1 million viewers

Filming locations[]

  • Ursula Street, Battersea, London (Outside Vanessa's house)
  • Cadogan Pier, Chelsea Embankment, London (the barge the Doctor lands his TARDIS on)
  • Amersham Road (A413), Denham, Buckinghamshire (the main road the Doctor lands the TARDIS next to)
  • Albert Bridge, London (location where the Watcher first beckons from)
  • Crowsley Park BBC Receiving Station, Blounts Court Road, Sonning Common, Berkshire (doubled as the Pharos Project for some external shots)
  • BBC Television Centre (TC3 & TC6), Shepherd's Bush, London

Production errors[]

If you'd like to talk about narrative problems with this story — like plot holes and things that seem to contradict other stories — please go to this episode's discontinuity discussion.
  • After Tegan closes the front door of Aunt Vanessa's house in part one, when she is shown returning to Aunt Vanessa's car, the front door of the house is visibly open again in the background.
  • When the Master puts the mind control bracelet onto Nyssa's wrist, part of it falls off.
  • In part four, when the Master enters his TARDIS, his shadow stays after it dematerialises.
  • At the beginning of part two, when the Doctor and Adric are going back to the TARDIS to escape the policemen, the Doctor opens the door to the right, but Adric goes through a door that is open to the left.
  • When the policemen open the police box and find that the Doctor and Adric have vanished, there do not appear to be any windows in the rear wall. This may have something to do with the shot in part one, where the Doctor exits the TARDIS from the back, due to the dimensional anomaly.
  • When the TARDIS is shrunk, it is first seen without the police box instruction plate. Later, as the shrunken TARDIS is carried away to the Central Registry by the Logopolitans , the instruction plate is there.
  • Near the end of part four, whilst the Doctor is crawling across the gantry of the satellite tower, you can easily tell the image of the Master in the doorway behind the Doctor is a photographic blowup because he doesn't move at all, you can't see behind him well and it doesn't at all look lifelike.
  • The Doctor reaches out an arm toward the Watcher before regenerating, but when the Fifth Doctor sits up both his hands are resting on his chest.
  • When the Master's TARDIS dematerialises at the end of part four, a light illuminates on the control panel in the background, showing that the dematerialisation is simply a fade between shots.


Home video and audio releases[]

DVD releases[]

This story was released on DVD as part of the New Beginnings box set, alongside The Keeper of Traken and Castrovalva.

Special Features[]

Blu-ray release[]

This story was released alongside the rest of Season 18 on the 18th of March 2019 as part of The Collection range. This release contains remastered film footage from their original elements and upscaled studio footage in order to present this serial in HD.

Special Features[]

  • Audio Commentary by actors Tom Baker and Janet Fielding and writer Christopher H. Bidmead.
  • Info Text
  • Isolated Music Soundtrack
  • Optional Updated Special Effects - Including new footage filmed at Jodrell Bank.
  • Hanging on by a Thread - Making-of Documentary. New for 2019, With Tom Baker, Janet Fielding, Sarah Sutton, Matthew Waterhouse, Christopher H. Bidmead, June Hudson, Adrian Gibbs (The Watcher), Paddy Kingsland (Music), Malcolm Thornton (Designer) and Margot Hayhoe (Production Manager).
  • A New Body at Last - 2006 DVD 50-minute documentary, featuring Tom Baker, Peter Davison, Sarah Sutton, Matthew Waterhouse, John Black, Peter Moffat, Christopher H. Bidmead & Adrian Gibbs.
  • Behind the Sofa
  • Studio Footage - Go behind the scenes of the regeneration.
  • Audio Restoration - A brief look at restoration work on this story.
  • Tomorrow's Times - Press coverage of the Fourth Doctor's era.
  • Stripped For Action - The Fourth Doctor's comic strips.
  • Doctor Who Stories - A 2003 interview with Tom Baker.
  • BBC1 Continuity Announcements
  • The Five Faces of Doctor Who - Trailer for the repeat season screened in 1981.
  • HD Photo Gallery
  • PDF Written Archive
  • Science Featurette - Entropy explained.

VHS Release[]

The story was released on VHS on 2 March 1992.

External links[]