Doctor Who: Terror of the Zygons

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Terror of the Zygons is the opening serial of Season 13 of Doctor Who, first broadcast in four weekly parts on BBC1 from 30 August to 20 September 1975. It was written by Robert Banks Stewart and directed by Douglas Camfield. It stars Tom Baker as the Fourth Doctor, Elisabeth Sladen as Sarah Jane Smith, Ian Marter as Harry Sullivan, and Nicholas Courtney as Brigadier Lethbridge-Stewart.

Summoned to Scotland by UNIT after a run of oil-rig disasters, the Doctor, Sarah, and Harry uncover a secretive village, strange organic technology, and a shape-shifting enemy, the Zygons, who plan to use their giant creature, the Skarasen, to strike at Earth. Identities are copied, trust is shaken, and the Brigadier leads the counter-attack while the Doctor follows clues from the loch to a hidden command ship.

Episode 1

North Sea oil rigs keep collapsing without warning, so the Brigadier summons the Doctor, Sarah, and Harry to UNIT’s makeshift HQ in a Scottish village by a brooding loch. Survivors talk about a vast shape rising from the water, and a slick of strange organic residue clings to broken metal hauled ashore.

The local laird bristles at soldiers on his land, while a calm nurse at the small hospital takes charge of an injured Harry with just a little too much interest. The Doctor prowls the moors and boat sheds, finding a pulsing transmitter tucked under a pier: something is calling to something else. At night another rig goes down; sonar records a gigantic moving contact. Sarah follows a whisper of clues to a locked store and glimpses a human shape peel and ripple like rubber: someone here is not who they seem.

The Doctor tests fibres from the residue and gets a reading that feels alive. A farmhand swears he saw a scarred “poacher” twice in two places at once. Back at the hospital, the nurse wheels Harry away for “tests.” In a creaking barn, the Doctor turns at a damp breath on his neck as a red, sucker-ridged figure steps from the shadows and strikes.

Episode 2

The Doctor survives and realises the attacker matches a legend from spacefarers: a Zygon, a shapeshifter that steals identities. Sarah sneaks into the hospital to check on Harry and discovers a secret passage behind a linen cupboard that slopes down toward the loch, warm and organic under her hands. The nurse corners her; Sarah dives through a hatch and tumbles into a biomechanical chamber pulsing like a heart.

The Zygons have a hidden ship under the water, and inside it humans lie cocooned as pattern sources for stolen faces. Their leader boasts of a symbiotic monster they control: the Skarasen, a colossal, armour-skinned creature they milk for nourishment and use as a weapon. On shore, UNIT traces intermittent signals and prepares depth charges, but the enemy is already out among them, wearing borrowed faces and whispering orders.

The laird’s authority is used to move troops, while a “villager” sabotages a convoy radio. Sarah is recaptured and strapped to a living console; the Doctor is dragged in to watch as the Zygons send the Skarasen to strike again. Out on the black water a wake swells and splits around something ancient. The Brigadier’s men ready rockets. The Zygon command room throbs: and the Skarasen answers its call.

Episode 3

Dawn shows twisted metal where another rig stood. The Doctor bluffs and bargains, learning the Zygons crashed centuries ago and now plan to take Earth, beginning with an attack that will panic the world’s energy powers. They will travel to London under a perfect disguise and summon the Skarasen up the Thames during a major conference.

Sarah wriggles free, releases Harry, and they drag the Doctor out through a mucus-slick service tube as UNIT depth charges boom across the loch. The organic hull spasms; parts of the ship collapse. On land, a familiar figure strides into the village hall (a respected aristocrat) yet the Doctor quietly notes a tiny wrongness in his manner. He deduces the Zygon leader has replaced the laird and is heading south by helicopter to oversee the strike.

Believing the underwater craft destroyed, UNIT loosens its grip: too soon. A surviving Zygon triggers a homing beacon; the Skarasen stirs and begins to track a portable control device toward the capital. The Doctor, Sarah, and Harry race for London, piecing together how to jam the signal. In the city’s bustle, security swarms the conference venue. On the river, a bulge ripples against the current, and a long, ridged back breaks the surface.

Episode 4

London holds its breath as the Skarasen pushes up the Thames, jaws working, horns glistening with spray. Inside the conference centre, the laird’s double directs officials into place, preparing to broadcast the lure that will bring the creature crashing through glass and steel. The Doctor and Sarah confront him; his face flows into Zygon form and a hooked weapon blooms from his arm.

UNIT barrels in. Shots crack; the leader falls, clutching the control pod. Outside, the Skarasen hesitates, confused. The Doctor snatches the device, retunes it, and sprints to the riverbank with Sarah at his heels, using the signal like a whistle to draw the monster away from the crowds. The creature surges toward them; at the last moment the Doctor hurls the pod. The Skarasen gulps it down, the command tone silences inside its belly, and the beast wheels, instinct pulling it homeward.

Back in Scotland, UNIT raids the Zygon hideout; without their leader and beacon, the remaining shapeshifters fall. The villagers emerge shaken but safe, and the loch lies quiet, keeping its secret. The Brigadier tidies up statements with practised calm. Harry decides to return to London the slow way, by train. The Doctor tips Sarah a grin, and the TARDIS fades into the mist.

Themes

As a mood piece and a statement that Season 13 means business, Terror of the Zygons is thunderously assured: briny, paranoid, and beautifully weird. The misty Highlands, the body-snatcher dread, and Tom Baker’s playful severity make it one of the era’s most atmospheric hours.

It doesn’t quite carry the cosmic weight of Genesis of the Daleks or the grand operatic sweep of Pyramids of Mars, but it sits comfortably near that top shelf, ahead of leaners like The Sontaran Experiment and more straightforward romps. If Robot announced a new Doctor and The Ark in Space announced a new tone, Terror of the Zygons announces a new confidence: the show can be folkloric and modern, intimate and epic, all in the same breath.

It also links past and future with uncommon grace. UNIT and the Brigadier step forward for a last great bow, tying Baker’s tenure back to the Pertwee years of The Invasion and The Green Death, while Harry’s departure subtly resets the TARDIS dynamic and points the team toward the space-gothic run of Planet of Evil and Pyramids of Mars.

Decades on, the Zygons’ one-and-done mystique makes their revival in The Day of the Doctor and the two-parter The Zygon Invasion/The Zygon Inversion feel richly earned. By the final fade, the programme has shed its Earthbound skin without losing its roots, standing poised for a season of stories that are darker, stranger, and very hard to forget.

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This is a chapter from Craig Hill’s book “Doctor Who – The Fourth Doctor”, chronicling every episode featuring the Fourth Doctor. It is available on Amazon.

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To view the list of other Doctor Who serials, please click this link

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