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. 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' Cloister Bell. This was also Anthony Ainley's first full story as the Master.

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

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Synopsis Edit

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.

Plot Edit

Part one Edit

A policeman is talking from the telephone of a police box in a lay-by, as a TARDIS materialises around it in disguise. Suddenly, the phone goes dead, the 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.

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.

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 police officers, led by a Detective Inspector, who have found the shrunken, dead bodies of Tegan's aunt and the other policeman. The Doctor realises that the Master has escaped from Traken and must be somewhere nearby.

Part two Edit

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. In the distance, a mysterious, white-clad stranger watches the proceedings. 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. This disrupts 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 Edit

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. Meanwhile, Nyssa has been brought from Traken by the Watcher, the mysterious white figure the Doctor spoke with. 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 through the scanner and correct the fault. The Doctor emerges from the restored TARDIS and tells Tegan that her aunt is dead. 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.

The Master attaches a device to the sonic projectors and sets up a counterwave 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. 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 finding 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 Edit

Adric, Nyssa and Tegan enter the TARDIS. The Doctor has the Watcher take it out of space/time. However, Tegan refuses to cooperate and follows the Doctor, Master and 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, 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 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.

Cast Edit

Crew Edit

References Edit

Astronomical objects Edit

Traken and Mettula Orionsis (Traken's star) are mentioned.

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 Edit

The Doctor misquotes his "old friend Huxley" by saying, "“The chess-board is the world; the pieces are the phenomena of the universe".

The Doctor mentions the second law of thermodynamics and entropy.

The Doctor Edit

Individuals Edit

The Doctor has taught Adric how to read Earth characters. (This is confirmed by Adric reading the police box instruction plate aloud in part one, and later telling the Monitor 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 can be seen in her room.

Locations Edit

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

Species Edit

The Logopolitans are vital to the stability of the universe. They discovered long ago that the Universe had passed the natural point of total collapse and so used block transfer computation to create Charged Vacuum Emboitments into other universes.

TARDIS Edit

Technology Edit

Story notes Edit

Closing credits Edit

At the end of part four:

Ratings Edit

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 Edit

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 motorway 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 Edit

narrative problems with this story — like plot holes and things that seem to contradict other stories — please go to this episode's discontinuity discussion. If you'd like to talk aboutproblems with this story — like plot holes and things that seem to contradictstories — please go to

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 it is wheeled away, the 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 comes on on the control panel in the background, showing that the dematerialisation is simply a fade between shots.

Continuity Edit

Home video and audio releases Edit

DVD releases Edit

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

Special features include:

Region 2 UK cover New Beginnings boxset Region 1 US cover

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 include: