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Terror of the Zygons was the first serial of season 13 of Doctor Who. It had been originally produced to conclude season 12 and saw the last regular appearance of Ian Marter as Harry Sullivan and was the first UNIT story since Robot. Although two more UNIT stories followed later this season, this was the last appearance of the Brigadier until 1983's Mawdryn Undead.

Originally a six parter entitled The Secret of Loch Ness, it was condensed down to four by script editor Robert Holmes; no significant plot threads were lost in the rewriting. (INFO: Terror of the Zygons)

The ending of the TV special Disney Time, broadcast just a few days earlier, was designed to tie into the beginning of the serial, as it showed the Doctor receiving the message which sends him to the Brigadier at the beginning of Terror of the Zygons.


Having received an urgent request for assistance from the Brigadier, the Doctor, Sarah and Harry arrive in Scotland, where they discover that a mysterious force has destroyed three oil rigs.

The mystery deepens when a piece of wreckage is found with giant teeth marks on it. The trail leads them to the shores of Loch Ness where they find that the legendary monster really does exist — and is the murderous tool of the Zygons, aliens intent on overpowering the planet.

The Doctor, his companions and UNIT must find a way to defeat the deadly Loch Ness Monster and its controllers, but the Zygons have the terrifying power to change shape. The Doctor's life has never been in more danger, as the line between allies and enemies is tested to the very limit...


Part one[]

On an oil rig off the coast of Scotland, a strange, high-pitched beeping sound echoes through the structure. The rig begins to break apart, collapsing into the North Sea. A radio operator tries to send a mayday, but his efforts are in vain.

The Fourth Doctor, Harry and Sarah hitch a ride with a motorist to the town where the Brigadier and UNIT have set themselves up in an inn. The Brigadier is talking to Huckle, an official of Hibernian Oil, who owned the rig. Huckle complains that three rigs have been destroyed in the last month, two of them belonging to Hibernian. The Brigadier assures Huckle that UNIT is also concerned, especially about the loss of life.

The Doctor, Harry and Sarah arrive at the inn. It turns out that the man who has given them a lift is the Duke of Forgill, a local landowner. The Duke is angry about Huckle's men trespassing on his land. Huckle assures him that he has warned his employees about this, and any who are caught will be dismissed without question. However, the Duke warns that any of Huckle's men caught on his land will be shot. He also wants to know what UNIT are doing here, but the Brigadier says that it is a sensitive matter. Though not pleased, the Duke leaves.

On the shoreline, a survivor of the destroyed rig washes up, barely alive.

The Brigadier brings the Doctor, Harry and Sarah to Hibernian Oil, where Huckle briefs them on the injuries of the rigs' crew. Harry decides to examine the injuries at the sickbay, while Sarah goes to talk to some of the locals. Huckle cannot understand it: the rigs were designed to be unsinkable and the seas were calm and empty before the incidents. The Doctor darkly notes that the sea may be calm but is never empty.

Back at the inn, Sarah talks to Angus, the landlord. She admires a stuffed stag's head above the fireplace, a gift from the Duke just this past week. Angus observes that the Duke has not been himself since the oil companies came. His servants have all left to go and work for them, leaving Forgill Castle cold and empty. He tells Sarah about Tulloch Moor and people disappearing over the centuries when the mist comes down. Sarah is sceptical — evil spirits do not destroy oil rigs. All this while, something alien watches Angus and her on a monitor screen.

The Duke's man, Caber, sees the rig survivor, Munro, stagger from the surf. Harry is driving by and goes to Munro as he collapses. Before Munro can tell Harry about what smashed the rig, Caber fires a rifle, killing Munro and creasing Harry's forehead with a second shot. Harry falls, unconscious. Back at the inn, the Doctor is working on a radio probe to check for localised jamming when a call comes in informing them about Harry.

Alien hands manipulate strange, organic controls. A high-pitched beeping summons a creature from the depths. It heads towards the Ben Nevis rig. The rig's communications with Huckle are jammed.

The Doctor and Sarah visit Harry, who is sedated and being tended by Sister Lamont, the nurse. The Brigadier arrives to tell him of the Ben Nevis rig's destruction. Sarah stays with Harry while the Doctor goes with the Brigadier. Outside, the Doctor spots wreckage from the rig with odd holes in it. He asks RSM Benton for plaster of Paris and makes a mould of the holes, revealing that something with very large teeth bit the rig. The watching aliens decide that the Doctor knows too much and must be destroyed.

Harry awakens. Sarah goes to tell the Doctor while Sister Lamont tells Harry he will be very well looked after. A high-pitched beeping echoes through the room, and Harry looks up in fear. As Sarah calls the Doctor, a suction-tipped hand clamps down on her shoulder. She turns as she is grabbed by a large, orange biped creature.

Part two[]

The Doctor hears Sarah's cries over the telephone and rushes to the sickbay. Sister Lamont tells them that she found Sarah gone and Harry's bed empty. The Doctor snoops around and finds Sarah unconscious in a decompression chamber. As Sarah comes round and starts telling the Doctor about what happened, a Zygon locks them in and starts to remove the air from the chamber. To escape death, the Doctor hypnotises Sarah into not needing to breathe and then puts himself in a similar trance.


The Zygons spy on the Doctor.

Harry is brought to the Zygon ship deep underwater, where he meets their warlord, Broton. Centuries ago, their spaceship was damaged, and they landed on Earth. They were waiting for rescue when they heard that their world had been destroyed in a stellar explosion. Now, they intend to claim Earth for their own, using the sea monster under their command, an armoured cyborg of great power. Broton explains that the Zygons depend on the lactic fluid of the Skarasen. Harry realises that if the monster is destroyed, the Zygons will die. Broton declares that no human weapon can affect the Skarasen.

The Brigadier is briefing one of his officers at the inn when gas floods the room, knocking them all out. Meanwhile, Sergeant Benton has found the Doctor and Sarah. He opens the pressure door. The Doctor exhales, awakens and carefully revives Sarah. He tells Benton that the trance was a trick he picked up from a Tibetan monk.

The Doctor, Sarah and Benton find the entire village has been drugged by some kind of nerve gas, but the people soon revive. The Doctor deduces that this was done so that something could get around unseen. The Zygons watch Huckle give the Doctor a device he found in the wreckage: the signal device that summons the Skarasen. Broton says that it must be recovered. Harry is taken to another room in the ship, where he sees other humans hooked up to booths, providing the Zygons with "body prints" that they use to assume human form.

The Doctor hypothesises that the signal device sends out a primeval mating call to attract the beast. The savaged body of a UNIT soldier is found on the moor, and the Doctor and the Brigadier go to see it, leaving Sarah behind in case Harry turns up. He does, but it is his Zygon duplicate Madra. He takes the signal device, saying that the Doctor asked him to collect it. Sarah notices his curious behaviour and questions him, but he pushes her aside and runs away. Sarah and some soldiers pursue him.

Sarah discovers "Harry" hiding in the upper level of a barn, and he attacks her with a pitchfork. She steps aside at the last moment, and he falls, impaling himself on his weapon and turning back into a Zygon. The signal broken, Broton realises that Madra is dead and remotely disperses the corpse. Harry, however, is freed from his body print booth.

Sarah wonders how the aliens knew they had the signal device. The Brigadier orders the inn searched for bugs. Broton in turn orders the Skarasen unleashed, even if it reveals their presence. The signal device begins to beep. The Doctor grabs it to lure the creature away, while the Brigadier tries to get a fix on the activating signal.

The Skarasen catches up to the Doctor on the moor, and he finds that he cannot get rid of the semi-organic signal device which has fastened itself to his palm. The Brigadier traces the incoming signal to Loch Ness. As the Doctor stumbles, Broton orders the Skarasen to destroy him.

Part three[]

Harry rushes into the Zygon control room and randomly hits controls, making the device fall off the Doctor's palm and allowing him to roll out of the Skarasen's way. Since the device is dead, Broton assumes that the Doctor is too and recalls the Skarasen. The Doctor retrieves the device and makes his way back across the moor as the Skarasen glides away. In the ship, Harry is dragged away by the other Zygons.

The Doctor is met halfway by the Brigadier and Sarah, who tell him that the signal came from Loch Ness. The Doctor decides to visit Forgill Castle, right next to the loch. They get a frosty reception from the Duke, who does not believe them about the monster or the aliens and is unhappy with their intention to drop depth charges in Loch Ness.

At the inn, Angus discovers the Zygon surveillance link in the stuffed deer head that was the Duke's gift. As he tries to pry it loose, Sister Lamont enters the inn. The sister turns into a Zygon and kills him, removing the link after. Angus' dying cries are heard by Benton and some UNIT soldiers, who discover the body and pursue the killer. The UNIT troops sweep through the nearby forest and fire on the Zygon.

The Brigadier is told that a Zygon is being cornered. He and the Doctor leave Sarah at the castle to research the monster. In the woods, the wounded Zygon disguises itself again as Sister Lamont and fools a UNIT soldier long enough to knock him out and steal his jeep. At the inn, the Doctor notices the missing eye in the deer head and realises that the Duke may be a Zygon facsimile.

At the castle, Sarah examines the upper bookshelves. She triggers a hidden switch, and a section of the bookcases slides open, revealing a passage. She takes a torchlight and goes in, following a long dark tunnel that leads to the Zygon ship. "The Duke" (in reality Broton) finds the open bookcase. He and "Caber" take the wounded "Sister Lamont" (the Zygon Odda) into the ship; the crew must be alerted and the intruder found and destroyed.

Sarah finds the cell where Harry is held. She frees him, and they sneak back to the castle, just in time to meet the Brigadier and the Doctor. Sarah tells the Brigadier about the Zygon ship. The Doctor enters the tunnel but does not get far; a scream is heard. The Zygons emerge in their true forms. Broton tells the humans that they are leaving with the Doctor as their prisoner. He warns them that the oil rigs were only a test; the "big event" is yet to come. Broton retreats, sealing the entrance to the tunnel.

The Brigadier orders the loch depth-charged to bring the Zygon ship to the surface. The Zygon ship does rise but keeps on rising into the sky, flying away.

Part four[]

Broton orders a jamming signal transmitted to block the humans' radar systems. The Brigadier prepares to move his troops out, but Sarah and Harry suggest they search Forgill Castle before they leave for clues to the Zygons' plans. Sarah finds some papers that indicate the Duke is the President of the Scottish Energy Commission, but Harry dismisses the information as useless. They return with the Brigadier to London.

The Zygon ship lands in a disused quarry. UNIT cannot track it. Radar stations are knocked out all over the country. However, there are reports of a large underwater object heading south at high speed. Broton enters the Doctor's cell and, taking the Duke's form again, tells him that Phase I of the conquest of Earth is complete. A great Zygon refugee ship is on its way but will take some centuries to arrive. In the meantime, Earth's environment must be restructured with human labour and Zygon technology to turn it into a new homeworld.

Left alone, the Doctor rigs some of the organic technology in his cell, electrocuting himself but sending a transmission to help UNIT track the ship to the quarry. By the time Broton and his men open the Doctor's cell door, the Doctor is apparently dead. However, when Broton leaves, the Doctor comes to. He makes his way to the body print chamber and frees the real Duke, Sister Lamont and Caber.

Broton leaves the ship to plant a trilanic activator on his target, which the Skarasen will then destroy, proving the power the Zygons hold. When Phase II is complete, he will broadcast his demands to the world. Inside the ship, the Doctor uses his sonic screwdriver to set off the fire sensor, triggering an alarm. When the Zygons go to investigate, the Doctor ushers the humans out of the ship, jamming the hatches and activating the ship's self-destruct.

Cast ensemble

The Doctor, Sarah Jane, Harry, the Brigadier and the Duke of Forgill look upon the TARDIS.

The Brigadier has arrived, and the escapees reach UNIT's position. The Doctor shouts for everyone to get down, just before the Zygon ship explodes. However, Broton is still free and has control of the Skarasen. The target is in London and must be close to the River Thames.

The Brigadier says the Prime Minister will be at a conference at Stanbridge House, near the river. The Duke adds it is the first International Energy Conference, with delegates from all over the world. As the Duke is the President of the Scottish Energy Commission, Broton will have a pass into the meeting. They leave for London.

"The Duke" places the activator in the basement of Stanbridge House. The Skarasen has been sighted mere minutes away. The Doctor finds Broton, back in his true form, who swears he will make sure the Doctor is dead this time and attacks him. Sarah calls for the Brigadier, who arrives to shoot Broton dead. The Doctor finds the trilanic activator in his pocket and feeds it to the Skarasen as it rises out of the Thames. After it consumes the device, the beast sinks back into the river and heads back to Loch Ness, the only home it has ever known. However, it is witnessed by not only the Doctor, Sarah and Harry, but many terrified Londoners.

Returning to Scotland, the Brigadier tells the Duke that the incident will be kept quiet, even the appearance of a fifty foot monster in the Thames. The Doctor leads them into the woods to the TARDIS and offers all of them a lift. The Brigadier and Harry decline. Sarah agrees on the condition they go straight back to London. The Doctor promises, and the TARDIS takes off with the Doctor and Sarah inside. The Duke tells the Brigadier that, as a Scotsman, he should have gotten a refund for Sarah and the Doctor's return train tickets.


Uncredited cast[]


Uncredited crew[]


The Doctor's items[]




  • The Zygon ship operates on a dynacron thrust via organic crystalography.



  • Robert Banks Stewart was largely unfamiliar with the series, so he wrote the Doctor, Sarah and Harry in the style of the main characters in The Avengers, which he had previously written for.

Story notes[]

  • This story had working titles of: Loch Ness, The Secret of the Loch, Secret of Loch Ness, The Loch Ness Monster and The Zygons.
  • This story was originally planned to end season 12, but was pushed back to the start of season 13 to allow the series to shift its broadcast schedule from a January start (its routine since 1970) to September.[1]
  • Nicholas Courtney is credited as "Brigadier" in Radio Times for part four.
  • Radio Times credits John Woodnutt as "Duke of Forgill" for part one, "Broton" for parts two and three, and "Broton/Duke of Forgill" for part four. All on-screen credits read "Duke of Forgill".
  • The Radio Times programme listing for part one was accompanied by a black-and-white illustration by Frank Bellamy depicting the Doctor in his tam-o'-shanter, the oil rig being destroyed and the Skarasen's eye, with the accompanying caption "A tartan touch for Dr. Who when he faces a new breed of monsters that bring terror to the North Sea: 5.45".
  • Radio Times art editor David Driver commissioned a full colour illustration from Frank Bellamy — depicting the Zygon spaceship taking off, the Doctor and the Skarasen, with a comic strip style speech balloon for the Doctor reading "WE'RE DEALING WITH A CREATURE THAT IS NOT OF ORDINARY FLESH AND BLOOD..." — in the hope it would be used as a front cover for the forthcoming 30 August–5 September 1975 issue to tie-in with the start of season 13. This never happened, but the artwork eventually saw print as part of Still waters, a two-page Radio Times article by Andrew Haden-Guest about the Loch Ness monster which featured in that issue. The introduction for the article read "Dr. Who / Saturday BBC1 / What is Nessie? Who can tell? In a new series starting this week, Dr. Who takes on the unidentified incumbent of Loch Ness. Here Anthony Haden-Guest plumbs the depths of the Scottish mystery". (original published text)
  • This is the only season opener to feature a companion departure, though Harry would return later in season 13 for The Android Invasion.
  • The departure of Harry while Sarah remains with the Doctor marks one of only two incontrovertible times in the televised classic series that a companion, who had already been with the Doctor before another one joins, remains with him after the second companion leaves. Jamie arrived before Victoria Waterfield and remained after her departure. Two other arguable examples would be Katarina and Sara Kingdom, who weren't with the Doctor very long, and ended up dying. Generally, the Doctor's roster of companions revolves fairly consistently.
  • This was the only on-screen appearance of the Zygons, save for flashbacks and verbal references, during the classic series. A Zygon was apparently to have appeared, along with a Dalek and a Cyberman, among the alien prisoners on the Time Lords' prison planet in Douglas Adams's original script of Shada, but the scenes set inside Shada itself were never recorded. The Zygons made their first on-screen appearance in the revived series in the Doctor Who 50th Anniversary episode, The Day of the Doctor, an episode which also featured the return of Tom Baker in a special cameo.
  • On the DVD release of this story, it featured a deleted scene set at the start of the story featuring the TARDIS materialising invisibly due to a faulty fusion plate. It was in a mixture of colour and black-and-white, but the monochrome sections were recoloured manually by the YouTuber Stuart Humphryes, a.k.a. Babelcolour, who also worked on The Mind of Evil and Genesis of the Daleks DVDs. The original unrestored colour and black-and-white version is included on the DVD as an Easter egg.
  • Margaret Thatcher had been elected Leader of the Conservative Party in February 1975, a few weeks before the story began production. Knowing that the UNIT stories were intended to be set a few years in the future, Nicholas Courtney ad-libbed the reference to the Prime Minister as “Madam” to suggest Thatcher was in office by the time the story was set.
  • This is, effectively, the earliest Doctor Who story directed wholly by Douglas Camfield to survive in its entirety. On Planet of Giants, Camfield only directed the final episode whilst on Inferno he did not direct most of the studio scenes due to falling ill with a heart condition. The Crusade, The Daleks' Master Plan, The Web of Fear and The Invasion are all missing episodes; and The Time Meddler is missing approximately twelve seconds of footage from its last episode, "Checkmate".
  • The scripted version of the scene where the Doctor and Sarah are locked in a decompression chamber required a practical special effect that was too expensive, so it was discarded and Tom Baker and Elisabeth Sladen were allowed to devise their own scene.
  • Nicholas Courtney recalled that his relationship with Tom Baker changed during the shoot, but not for the better. "He was less congenial, and hyper-sensitive to criticism. I think he was off on his own plane, and the rest of us had to scramble to keep up with him". According to Courtney, "the tension turned ugly once", when Baker was handed some uncomplimentary notes and lashed out. "He'd had the part for a year and didn't take kindly to being treated like an incompetent neophyte".
  • Nicholas Courtney suggested to Philip Hinchcliffe that the Brigadier be killed off in this story, as he felt he would no longer be required in the show's new format. Hinchcliffe turned down the idea, however, feeling that it would be an inappropriate fate for a character who had been so vital to the programme.
  • The script originally placed a far greater emphasis on the Skarasen and the loch. Robert Holmes felt that the Zygons were more interesting characters as they could interact with the main cast.
  • Ian Marter found John Woodnutt funny in rehearsals, so location filming saw him giggly when he was supposed to be scared.
  • John Woodnutt spent a lot of time getting the Laird's accent right, pointing out that a Laird would probably have been educated at Eton and would therefore sound English. However, Douglas Camfield wanted a Scottish accent. The end result is a compromise.
  • Nicholas Courtney claimed to have been unhappy making the story, as he thought he would be playing the Brigadier for the last time. He felt sad that the character faded away in such a manner.
  • Philip Hinchcliffe thought this was where Tom Baker finally got his performance spot on.
  • This is the first television story since TV: The Dæmons to be penned by somebody who had never written for the series before.
  • Robert Banks Stewart wasn't interested in writing outer space stories, so he set the story in his native Scotland and used the Loch Ness Monster because he felt that its lack of detail made an ideal monster.
  • The original cliffhanger for Episode Two involved the Skarasen attacking the Doctor as he rowed upon its waters, rather than traversing Tulloch Moor.
  • Sister Lamont was originally named Sister White, Stansbridge House was originally named Stansgate House and Hibernian Oil was originally named Claymore Oil.
  • Douglas Camfield had taken a five-year sabbatical from the series having suffered a heart attack during the production of Inferno. He was lured back by the premise of this story.
  • Douglas Camfield found that, when moving, the Skarasen appeared more comical than threatening, and so he decided to use as little footage of it as possible. Instead, new material was written for part two which explained that the Zygons had deployed nerve gas on the denizens of Tulloch to allow the Skarasen to pass by unobserved.
  • The Doctor dons Scottish garb when arriving in Scotland. Four future actors to play the Doctor would be Scottish - Sylvester McCoy, David Tennant, Peter Capaldi and Ncuti Gatwa.


  • Part one - 8.4 million viewers
  • Part two - 6.1 million viewers
  • Part three - 8.2 million viewers
  • Part four - 7.2 million viewers

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.
  • When the Doctor is running from from the Skarasen, he leaves open the driver's door to the Land Rover he was driving. Later, when the Brigadier and Sarah-Jane drive by, both the driver's and passenger's doors of the Land Rover are closed. (Although the camera turns away, following Tom Baker, you can just hear the sound of the door swinging shut.)
  • While the Doctor and the Zygons' captives are running away from the Zygon spaceship before it explodes, the ship's shadow moves.
  • When the Brigadier and the Doctor examine the dead soldier's body in part two, one of the soldier's fingers moves.
  • When the Caber jams the door of the Zygon ship by breaking off one of the mechanisms of the control panel, the whole wall of the ship shakes.


DVD, Video, CD and Laserdisc releases[]

DVD releases[]

A DVD was commissioned in April 2011, and subsequently announced for release in the UK on 30 September 2013. However, an "advance release", minus extra features, was also announced for release on 29 July 2013 as part of the UK-exclusive The Fourth Doctor Time Capsule box set, limited to 5,000 copies.[2] At the time it held the distinction of being the final complete classic-era story to see a DVD release, before The Enemy of the World was announced as having been found.

Special Features[]

VHS releases[]

This story was released as Doctor Who: Terror of the Zygons on VHS.


PAL - Polygram
PAL - BBC Video
PAL - BBC Video
  • USA 1991 (Movie Format - unconfirmed)
NTSC - Playhouse


  • Minor cuts were reportedly made on both the UK compilation and episodic releases to the scene in part two where Harry's Zygon replica threatens Sarah with a pitchfork in the barn, to obtain a "PG" certificate.
  • The 1999 episodic release also featured at the start of the tape footage of Tom Baker as the Doctor on the Summer Bank Holiday Monday edition of Disney Time, originally transmitted 25 August 1975.
  • The 1988 compilation video release was previously only available in Australia.

Laserdisc release[]


PAL - Encore Entertainment EE1203

CD release[]

External links[]