Doctor Who: The Sea Devils

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The Sea Devils is the third serial of Doctor Who Season 9, first broadcast in six weekly parts on BBC1 from 26 February to 1 April 1972. It was written by Malcolm Hulke and directed by Michael E. Briant. It stars Jon Pertwee as the Third Doctor, Katy Manning as Jo Grant, and Roger Delgado as the Master.

The Doctor and Jo visit a high-security island prison where the Master is held, just as ships vanish and workers on nearby sea forts report attacks from the deep. An ancient aquatic branch of the Silurians is awakening, and the Master schemes to turn their power against humanity.

With the Royal Navy drawn into the crisis, the Doctor tries for peace but must face fear, sabotage, and open conflict along the coast. It is Set around the British coast and incorporates naval collaboration.

Episode 1

The Doctor and Jo visit a high-security prison on a bleak sea-girt island to check on an old foe: the Master, urbane in a cell and purring that he has reformed. Shipping reports say something is attacking sea forts along the coast; the Master’s eyes glitter with amusement when the Doctor mentions it. On the mainland, a Royal Navy base commanded by Captain Hart coordinates search and rescue as a terrified survivor babbles about a reptile from the deep.

The Doctor and Jo helicopter to the last battered sea fort, picking through smashed gantries and claw-raked doors. A shadow moves under grating; a sleek, gilled head rises, eyes cold, and the Doctor whispers a name from prehistory: Sea Devils (aquatic cousins of the Silurians). Back at the prison, retired Colonel Trenchard fusses over national security and treats the Master as a VIP detainee.

The Doctor notices parts and tools going missing from naval depots; someone is assembling something big. He dives off the fort to trace sonar anomalies, glimpses a weed-shrouded tunnel, and is nearly dragged under by webbed hands. Hauled out coughing, he tells Hart this is no lone creature but a colony waking. On the prison CCTV, the Master watches, very pleased, and takes a call he shouldn’t be able to receive.

Episode 2

The Master plays Trenchard like a violin, claiming foreign saboteurs are raiding the coast and that only he can help trap them: if he’s allowed controlled freedom. Under that cover, hired men move equipment through the prison and out to sea. At the naval base, Jo pores over sonar charts while the Doctor returns to the fort with diving gear, following a power trace down a rock chimney into a natural cavern. There, he finds a pressure door of unknown alloy: and a Sea Devil sentry.

The creature attacks; the Doctor wriggles free and surfaces inside the fort as more Sea Devils swarm the legs. Depth charges arrive too late; the fort collapses into the tide. Meanwhile the Master strolls through a restricted stores dock and lifts a critical frequency modulator, cheerfully whistling children’s TV tunes as he goes. Captain Hart dispatches patrol boats to a newly mapped ridge; two fail to report back.

Trenchard starts to doubt his ally but doubles down, having Jo detained when she arrives asking awkward questions. The Master slips away in a fast launch to a rendezvous point marked by sonar beacons only Sea Devils should hear. On the horizon, a dark line of backs breaks the water and turns toward shore.

Episode 3

Sea Devils rise from the surf and overrun a small gun emplacement, their heat guns hissing, then melt back under the waves. Public panic builds; the government demands results. The Doctor tracks the thefts to the prison and confronts Trenchard, who blusters about patriotism until the Master saunters in with guards.

A barbed conversation becomes a bright, fast sword fight among display foils, the Master laughing as he presses the attack. He flees with his prize as Sea Devils storm the island; Trenchard, finally realising he has been duped, is shot trying to defend his flag. Jo frees the Doctor and signals the Navy as the creatures haul equipment down a weeded incline to their base. The Doctor persuades Hart to try diplomacy and descends alone through the sea tunnel.

In a cathedral-like chamber he meets the Sea Devil leader and argues for coexistence: two intelligent species sharing one world. The leader listens without warmth. Suddenly the Master steps from the shadows, all charm and treachery, and claims to speak for “the human military.” He proposes an alliance to wipe out mankind. The Doctor protests; the Sea Devils choose the safer ally: the one offering weapons. He is disarmed and marched away as a collaborator grins.

Episode 4

Dragged between worlds, the Doctor is forced to help the Master assemble a sonic device designed to broadcast through the deep and wake Sea Devil colonies across the oceans. He sabotages where he can, swapping leads and adjusting tolerances a fraction at a time. On land, a pompous civil servant named Walker arrives to take charge, orders lunch, and demands “vigorous action.”

The Navy’s first assault, depth charges and a net, provokes a counterstrike. Sea Devils in rafts raid the base, smash sonar rooms, and vanish, leaving flooded corridors and shaken sailors. Jo slips ashore near the prison ruins and follows drag marks to a cliff cave, finding proof of the Master’s comings and goings. In the undersea hall, the Doctor wins a private audience with the leader and argues again for peace.

The Master counters with footage of tanks and rockets and plays on old grievances from before the apes ruled. The leader grants the Doctor one chance to prove his claim that humans can be reasonable. He is escorted to the surface. and straight into Walker’s second plan: a barrage line that turns the channel into a maelstrom. The Doctor watches diplomacy drown and knows what the Master will say next: “You see? They only understand force.”

Episode 5

Walker doubles down, proposing a nuclear charge to “sterilise” the sea bed. The Doctor is appalled; Captain Hart looks sick. The Master activates his device. Low, seismic notes shudder through the water; in distant trenches, more Sea Devils stir and begin to march. A hovercraft roars in a spray of salt as the Master and his escort raid the base, snagging the last components they need and abducting engineers. Jo hides in a stores crate and is carried into the heart of the Sea Devil complex.

There she finds the Doctor, who quietly sketches a counter-scheme: let the broadcast complete, but lace it with a timed overload that will burn out the colony’s power at the source. To do it, he must finish the Master’s machine to perfection: then betray it in one pulse. On the surface, Walker commandeers a submarine and blusters about authorisation codes while Hart quietly evacuates civilians.

The Master parades Jo before the leader as proof of leverage and forces the Doctor to make the final connections. The device thrums, harmonics climbing. Across the world, sleeping armies open their eyes. The Master smiles, intoxicated by scale. The Doctor closes a last circuit with steady hands and hopes his arithmetic is kinder than Walker’s.

Episode 6

The broadcast peaks. The Doctor throws a concealed switch and the note flips into a scream only the machinery can hear. Capacitors flash white; control panels flower sparks; the sea cave trembles. The Doctor drags Jo into a side tunnel as the main hall erupts. On the surface, Walker’s nuclear bluff collapses in panic; the order is never sent.

Sea Devils surge toward the base one last time and are met by sailors with hoses and grit holding a line that finally holds. In the wrecked chamber, the leader confronts the Doctor; he bows his head, sorry that peace failed, and triggers the final fail-safe he buried in the power stack. The colony begins to self-destruct. The Doctor and Jo sprint for daylight, pursued by the Master, who dives for a waiting hovercraft and skims away under fire, saluting with infuriating cheer.

The cave mouth implodes; shockwaves flatten the surf; silence follows. Captain Hart calls off further attacks. Walker sputters about reports and slinks to a mess deck. The Doctor stands on the shingle, bleak: he tried to talk and ended by blowing up a city. Jo squeezes his arm. Somewhere at sea, other colonies may have heard, and waited. The Master is at large again. The tide flows in, indifferent and patient.

Themes

As a return to Earthbound monsters with a naval twist, The Sea Devils is a muscular sequel to Doctor Who and the Silurians. It is more kinetic than Day of the Daleks and moodier than The Curse of Peladon, if not as baroque as The Dæmons or as apocalyptic as Inferno.

Its open-water action, island espionage, and eerie undersea menace give Season 9 a different texture, and the Master’s needling presence keeps the stakes sharp. On balance, it lands solidly in the era’s upper tier: confident, atmospheric, and surprisingly bleak.

Link-wise, it threads past and future with care. Picking up after the Master’s capture in The Dæmons, it finds him imprisoned and scheming, his escape here pointing ahead to grander machinations in Frontier in Space and the Dalek entanglements of Planet of the Daleks. The plea for coexistence extends the moral line from Doctor Who and the Silurians and foreshadows the later tragedy of Warriors of the Deep.

The Earth politics and military complicity rhyme with The Ambassadors of Death and lead into the colonial critique of The Mutants. Even far later, the Silurian thread resurfaces in The Hungry Earth/Cold Blood, proving that the uneasy question posed by The Sea Devils (sharing a planet without war) never really sinks.

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

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