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The Armageddon Factor was the sixth and final serial of season 16. It concluded the season-long Key to Time story arc. It saw Mary Tamm make her final appearance as Romana I while her replacement, Lalla Ward, appeared in the story in a different role. This story also marked the first appearance of the Black Guardian, who would not be seen again until Mawdryn Undead, four years later.


The final segment of the Key to Time is at the heart of a devastating war between neighbouring planets Atrios and Zeos. The Fourth Doctor discovers that a sinister entity is manipulating events and the cost of obtaining the final segment may be more personal than he imagined.


Part one[]

The sixth and final segment of the Key to Time is on the planet Atrios. Twin planets Atrios and Zeos are locked in a long-running war. The young Princess Astra, nominal leader of Atrios, is appalled at the devastation and wants peace, but the Marshal, in charge of the war, actually possesses the power. The Marshal secretly confesses to his aide-de-camp Shapp that they are losing and their defences are becoming inadequate to repel the enemy's attacks. He is desperate for the edge that will bring victory, and, on instruction from an unseen entity, he leads Astra on a fool's errand into a trap, where she is abducted and transmatted away.

The Doctor and Romana I land on Atrios, and the Doctor's TARDIS is soon buried in rubble from a Zeon aerial bombardment. The Marshal finds them and believes them to be Zeon spies, along with Astra's lover, Merak. The Doctor tricks the Marshal to calling for K9, who knocks out the lights to let them escape. Returning to the place where they had landed, they find the TARDIS gone...

Part two[]

Merak has followed them, and they find Astra gone. K9, meanwhile, is lured away to be recycled. The Marshal is contacted by an unseen force, who tells him to treat the Doctor and Romana as guests. The Marshal implores the Doctor to assist Atrios. The Doctor proposes a shield that will stop the Zeons from attacking, but the Marshal insists he create a weapon for total victory.

Romana notices that the Marshal is acting under an outside influence when he accidentally shows a small device on his neck after flipping out when the Doctor runs to save K9 from the furnace. Afterwards, the Doctor asks the Marshal to send him to Zeos, to which the Marshal refuses. The Doctor reveals to Romana that something is probably blocking Zeos. Astra appears on a television and states that the Zeons will destroy Atrios if the Marshal does not surrender, however he refuses.

The Doctor once again asks the Marshal to allow him to go to Zeos and this time the Marshal informs him that there is a way. The Doctor then goes to a transmat room that will apparently take him to Zeos, but two figures in masks appear next to him. Romana runs in, yelling for the Doctor to warn him of the trap, but it is too late. The Doctor and the figures have gone.

Part three[]

The unseen entity tells Marshal that the war will stop, while the entity traps him in his domain. When the Doctor is brought to the entity, it introduces itself as the Shadow, and reveals that he has the TARDIS. After a failed attempt at trying to control him like he has controlled the Marshal, the Shadow asks the Doctor to open his TARDIS and bring out the other five segments. The Doctor bluffs that it is impossible to take the five segments out of the TARDIS without also having the final piece, but the Shadow does not trust this. He leaves the Doctor to "make his own mistake". Once the Shadow has gone, the Doctor decides to search for the sixth segment.

Meanwhile, Merak has transmatted to Zeos. Astra is on the ship in chains, being asked by the Shadow where the sixth segment is. Romana and K9 transmat to Zeos, following Merak. Shapp finds himself with the Doctor after also being transmatted and the pair reunite with K9, who has found the commandant of the Zeon forces. They meet up with Romana and Merak and K9 takes them all to meet the commandant, which is actually a supercomputer named Mentalis. The Doctor reveals that there are no Zeons on Zeos and then asks for information on the Princess Astra, but they find that any information concerning her is inaccessible.

The Marshal, meanwhile, has decided to attack Zeos, with himself leading the assault. In his spaceship, he prepares to launch the missiles to destroy Zeos...

Part four[]

The Doctor reveals that, because the Mentalis thinks the war is over, it cant counteract the Marshal's incoming attack, and rather than accept defeat, it will self-destruct, destroying both Zeos and Atrios — a concept known as the "Armageddon Factor".

The Doctor tries to dismantle the Mentalist and tells Merak and Shapp to return to Atrios and contact the Marshal. On their way to the transmat, Astra appears and, having been hypnotised by the Shadow, beckons Merak. Merek leaves Shapp and reaches for Astra, but passes straight through her, revealing her to be a projection. He begins falling.

Meanwhile, the Doctor accidentally triggers the Mentalis' primary alert function, and the computer becomes mindless by destroying its own control centre. Desperate to stop the Marshal's attack, the Doctor uses the five segments of the Key to Time, plus an artificial sixth segment made from chronodyne, to generate a temporary time loop around the Marshal's ship.

Realising that the Key is no longer safe, the Shadow sends Astra to retrieve it. She first collects Merak, telling him that she tried to save him, which, after a moment of confusion, he accepts. The pair find K9 but are shortly cornered by the Shadow's minions. K9 drives the minions away but is then hypnotised by a small device which takes the guise of a distress call. K9 is then transported away, where he is reprogrammed by the Shadow.

After abandoning Merak, Astra joins the Doctor and Romana in the TARDIS. The Doctor notices Astra staring at the Key to Time, and ask if she knows where the sixth piece is. He then pilots the TARDIS to a third planet, where the Shadow has been hiding. On the planet, the Shadow laughs that the Key to Time is his...

Part five[]

After arriving on the planet, the Doctor, Astra and Romana are all separated from one another. The Doctor finds another renegade Time Lord, his old classmate Drax, in the corridors and the two reminisce about their time at the Academy; the Doctor enquires about his old classmates' Cockney accent, and Drax informs him he was locked up in Brixton prison for ten years because of a fault in his TARDIS. Drax was employed with threat of death, and he was forced to build Mentalis. The Doctor persuades Drax to assist him, and they remove the control device from K9. Drax repairs his dimensional circuit.

Romana is captured by the Shadow and is tortured. The Doctor arrives and the Shadow demands he give him the Key, revealing that he has the sixth segment. The Shadow also reveals that he has been manipulating the entire war from his enormous vessel midway between the two planets and that he is an agent of the Black Guardian; he has been watching the sixth segment while waiting for the Doctor to collect the other five.

The Doctor goes to get the Key and tries to distract the Mute escorting him by saying the Shadow will kill him and his fellows. Drax then enters with the dimensional circuit and shrinks the Doctor down.

Part six[]

Drax also shrinks himself, and they decide to have one of them provide a distraction. However, the Doctor has left the TARDIS door wide open, allowing the Shadow to walk in and take the Key himself. He collects the Key and places it on a table. Astra reveals to Romana that her "destiny" is near and Romana realises that Astra herself is the sixth segment.

Meanwhile, the Doctor and Drax use K9 to sneak back into the Shadow's lair, with K9 still pretending to be under the Shadow's control. K9 reports to the Shadow that the Doctor and Drax have been eliminated and the Shadow basks in his victory as Astra transforms into the sixth segment. He goes to compose the Key, ignoring Romana's warnings that it will break the time loop surrounding the Marshal, but the Doctor and Drax return to normal size and take the Key and they all escape.

The Doctor and Drax disarm Mentalis just before the time loop expires, and, when the Marshal fires, the war rockets are deflected by a force field, destroying the Shadow and his ship instead. Hearing his minion's dying words, the Black Guardian disguises himself as the White Guardian, telling the dying Shadow that he will trick the Doctor into giving him the Key to Time himself.

Black Guardian Key to Time

"Doctor, you shall die for this!"

In the TARDIS, the Doctor has composed the Key and contemplates having absolute power over the entire universe. The "White Guardian" appears on the TARDIS monitor and congratulates the Doctor on a job well done. He then insists that the Doctor hand the Key over to him. When he rather callously dismisses Astra's sacrifice, the Doctor realises this is actually the Black Guardian in disguise and disperses the segments across the universe again, allowing Astra to reunite with Merak. The Black Guardian is furious and threatens to destroy the Doctor. However, the Doctor has installed a randomiser on the TARDIS console, ensuring that neither he nor the Black Guardian knows where he'll end up next.


Uncredited cast[]


Uncredited crew[]



  • Romana compares the "identification ritual" between K9 and Mentalis to the dance of the bees.
  • The Doctor compares the programming of Mentalis to the behaviour of a suicidal scorpion.

Astronomical objects[]

  • Atrios and Zeos are in the Helical Galaxy.
  • The Shadow operates on an artificial planet (called the third planet or the Planet of Evil) put between Atrios and Zeos.

Cultural references to real world[]

  • The Doctor mentions Christopher Columbus.
  • The Doctor mentions Troy.
  • The Doctor claims to have learnt the tricks of the fire walkers while in Bali.



  • Atrions are provided with hand-wrist Geiger counters called rad-checks.
  • On Atrios, there is a recycling shaft, able to work metal.
  • The Shadow uses a little black neck device for mind control.
  • Drax's TARDIS broke down on Earth due to a fault in its hyperbolics, but when he tried to repair it he was imprisoned for theft.

Time Lords[]


  • Disintegration capsules are used in the war to avoid prisoners.

Story notes[]

  • This story had the working title of Armageddon.[1]
  • Part one was the 500th episode of Doctor Who.
  • The final scene of this story was written, uncredited, by producer Graham Williams and incoming script editor Douglas Adams.
  • This story was the final six-part story broadcast until Dreamland in 2009. Two other stories during the classic series do come close, however. Shada was partially produced for the next season, but never broadcast and The Two Doctors, when sold internationally, was broken up from its format of 3 x 45 minute episodes into the more traditional 6 x 25 minute episodes.
  • According to Mary Tamm in the DVD featurette There's Something About Mary, it was while filming this serial that she made her final decision to leave the series. She jokingly suggested that Lalla Ward replace her.
  • Twenty-three minutes into transmission of part five, a technical fault on the playback equipment resulted in the programme going off the air for twenty seconds. The break occurred at the point where the Doctor is being escorted to the TARDIS by the Mute; and the Shadow makes to remove his control device from Princess Astra, saying "Now, Princess, your work is done. Your dest—". BBC continuity apologised to viewers for the breakdown in transmission, displaying a TEMPORARY FAULT caption slide and playing music, "Gotcha" by Tom Scott, better known as the theme music to NBC's cop buddy show Starsky & Hutch (1975-79), until the fault was rectified. When transmission was restarted, the 625 line PAL colour videotape had been slightly rewound so there was a repeat of the action immediately prior to the break — with the Shadow's previously interrupted line also finally completed as "Your destiny is at hand."
  • Pat Gorman (Pilot) is uncredited on-screen for part six, but credited in Radio Times.
  • Stephen Calcutt (Mute) is uncredited on-screen for parts five and six, but credited in Radio Times. His character was referred to as "Super Mute" in existing BBC documentation for the story.
  • Tom Baker got angry with the scripts. Michael Hayes later said: "I did actually crack. I got out of my seat in the production gallery and made for the studio floor with the full intention of flattening him. Luckily, it is a vast studio and there is a very long ladder down to the studio floor, and I had time to reflect on how terribly unproductive this would be. So I skidded to a halt in front of him and said, 'Tom, let's talk about this quietly,' which I think was a much better way to handle the situation!"
  • Public television station WYCC's August 19, 2017, broadcast of The Armageddon Factor mistakenly had the serial aired in a 1:1 aspect ratio rather than the intended 4:3, causing the video image to appear horizontally squashed for the entirety of the serial's duration.[2]
  • Roughly two months after this serial's broadcast, the anime series Mobile Suit Gundam first aired in Japan. Like this serial, it featured a faction called Zeons, though their uniforms bore closer resemblance to those worn by the Atrions. Most notably, Char Aznable's uniform closely resembles the one worn by the Marshal of Atrios.
  • Bob Baker and Dave Martin initially envisaged Drax as an elderly eccentric, thinking along the lines of the aged prisoner in The Count of Monte Cristo. Subsequently, they re-imagined him as a character in the mould of a South London car salesman. One of the inspirations for this approach was Trevor Ray.
  • In the original storyline, both Atrios and Zeos were populated. Astra (at that point called "Reina", a name later changed to avoid confusion with Prince Reynart from The Androids of Tara) was an astrophysicist who had discovered the Shadow's planet lying between the two warring worlds. The conflict had arisen because Atrios and Zeos blamed each other for a catastrophic shift in their orbits; they were being egged on by the Shadow, known as "the Presence" on Atrios and "the Voice" on Zeos. The Doctor was forced to use the makeshift Key To Time to temporally freeze both planets' armies. The Shadow's own shadow turned out to be the sixth segment of the Key To Time. His plan was to use the powers of the Key to pit one half of the universe in war against the other half. The Doctor stopped the Shadow by unfreezing the Atrian and Zeon armies and giving each the coordinates of the Shadow's "Castle of Evil".
  • The Black Guardian originally didn't appear in the climax. Originally, the Doctor simply decided that he did not trust the White Guardian with the Key, and consequently scattered the six segments again to prevent anyone from controlling it. This was changed when Cyril Luckham was unavailable to reprise his role. At one point, Luckham was supposed to play the Black Guardian.
  • The closing credits of part six feature the return of the section of the Doctor Who theme commonly called the "Middle Eight". This was previously done in the previous season finale, The Invasion of Time.
  • Bob Baker and Dave Martin took inspiration from the ongoing Cold War. As part of their research, they visited the Central Government War Headquarters, a thirty-five-acre underground complex in Corsham, Wiltshire which was built in the late 1950s to provide a refuge from which the British government could continue to operate in the event of nuclear war. Although the facility was normally off limits to the public, Baker and Martin were delighted to learn that the officer in charge was a fan of Doctor Who, and he arranged their tour.
  • The character of Drax was left over from an early script for The Hand of Fear, also written by Bob Baker and Dave Martin.
  • The idea of a person being segment of the Key to Time came from Douglas Adams for The Pirate Planet.
  • Part one of this story aired on Tom Baker's birthday.
  • At one point, it was going to be revealed that the Black and White Guardians were different aspects of a single entity.

Outtakes and gag reel footage[]

Several clips of scene performances not intended for broadcast have been circulated from this serial, including two sequences videotaped during rehearsal (Mary Tamm is seen wearing glasses and hair-curlers). In one scene, Tamm and Baker jokingly pretend to move in for a kiss after delivering a line, and in another widely circulated clip, the Doctor replies to a negative comment from K9, "You never f***ing know the answer when it's important!" Off screen crewmembers laughed at both of these outtakes.

It was also during production of The Armageddon Factor that Baker, Tamm and John Leeson filmed a brief one-minute gag scene dubbed "Doug Who?" for the BBC staff Christmas party. The scene begins with the Doctor and Romana sitting on the floor by the TARDIS console, apparently kissing off screen, and then acting tipsy as they share a bottle of vodka with K9, who is asked to sing a few bars of "We Wish You a Merry Christmas". The Doctor then asks K9 what he wants for Christmas; K9 replies and then asks the Doctor for what his desire is, to which the Doctor looks into the camera and then leers at Romana, who leers back before the two actors and the crew break into laughter.

To date, the rehearsal outtakes have not been commercially released, though they are widely available on video-posting websites. "Doug Who?", retitled "Merry Christmas Doctor Who", is included as a bonus feature in the expanded Key to Time DVD set released in 2007 in the UK and 2009 in Region 1.


  • Part one - 7.5 million viewers
  • Part two - 8.8 million viewers
  • Part three - 7.8 million viewers
  • Part four - 8.6 million viewers
  • Part five - 8.6 million viewers
  • Part six - 9.6 million viewers


  • Theta Sigma is the Doctor's real name. It's implied here and further established in TV: The Happiness Patrol that this is a nickname.
  • The outtake in which Tom Baker barks at K9 "You never f***ing know the answer when it's important" is sometimes described as an outtake from actual filming, and sometimes is used as an illustration of Baker's temperament on the set. In reality — as revealed from an actual viewing of the clip — it was simply a joke that occurred during a taped rehearsal (as evidenced by the fact Mary Tamm is not in full costume, is wearing her off-screen glasses and has her hair up in rollers).
  • Similarly, the rumour that Baker and Tamm filmed an unbroadcast kissing scene also stems from the existence of another rehearsal gag take, as well as the infamous "Doug Who?" skit (described above). Nothing of this sort was filmed for TV broadcast, nor was "Doug Who?" ever intended as part of the televised story either.
  • A longstanding myth holds that Mary Tamm revealed to the production team that she was pregnant and this led to her resignation during or after production of Armageddon Factor. This is openly contradicted by Tamm in interviews and the 2007/09 DVD featurette "There's Something About Mary" in which she states she chose to leave because she was no longer satisfied with the character of Romana and would have returned to film a regeneration if she'd been invited.

Filming locations[]

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.
  • Whenever the Marshal is "meditating" (and the entire mirror is in shot) a camera, and occasionally crew members, are visible in the far left hand side of the mirror.
  • In part two, after the TARDIS has left, it can still be seen behind Romana just after K9 starts blasting a door.
  • In the same scene, K9's laser beam is not properly aligned because the camera moves slightly.
  • In part three, Shapp's gun falls apart when it hits the floor.
  • In part four, the button in the Marshal's ship that fires the missiles is initially yellow but when the pilot presses it, it is now red.
  • In part four, when K9 exits the transmat, he's got the new left panel he gains in part five.
  • In part six, Astra regains the circlet Merak had used to distract the Mute.
  • In part six, one of the Mutes kicks up a piece of studio carpet.
  • In part six, when Drax is sitting next to K9 inside the TARDIS, the shadow of a boom microphone can be seen on the wall above his head.


DVD and video releases[]

DVD releases[]

Special Features (2009 version)[]

Disc One[]
Disc Two[]
  • Defining Shadows -The cast and crew look back at the making of this story, featuring interviews with writers Bob Baker and Dave Martin, designer Richard McManan-Smith, Lalla Ward (Astra), Davyd Harries (Shapp), and Barry Jackson (Drax)
  • Directing Who - Retrospective on Michael Hayes' work directing the serials The Androids of Tara, The Armageddon Factor and City of Death
  • Rogue Time Lords - A potted history of various errant Time Lords featured throughout the series
  • Pebble Mill at One - Tom Baker interviewed in 1978 promoting the broadcast of the 500th Doctor Who episode (The Armageddon Factor part one), plus an interview with Dick Mills and Brian Hodgson of the BBC Radiophonic Workshop, featuring the creation of sound effects for The Armageddon Factor
  • The New Sound of Music - Dick Mills talks about creating Doctor Who sound effects
  • Merry Christmas, Doctor Who - An infamous skit for 1978's BBC Christmas Tape filmed for BBC staff viewing only in which the Doctor and Romana get a little tipsy while celebrating the season and get K9 to sing a holiday song
  • Late Night Story - Tom Baker dramatically reads five spine-chilling stories from this December 1978 series, one never before broadcast, and seen here for the first time. Stories featured include "The Photograph" by Nigel Kneale, "The Emissary" by Ray Bradbury, "Nursery Tea" by Mary Danby, "The End of the Party" by Graham Greene, and the untransmitted "Sredni Vashtar" by Saki
  • Continuities - Off-air continuity announcements played before and after each episode of the serial during its original BBC1 transmission
  • Alternative/Extended Scene
  • Photo Gallery
  • Easter Egg: Footage of the transmission breakdown that took place during the original broadcast of Part Five. To access this hidden feature, press right at Continuities on the Special Features menu to reveal a hidden Doctor Who logo.


The Key to Time boxed set covers[]

Video releases[]

External links[]