This will entail the infiltration of Earth's defence systems and the provocation of another World War, more terrible than any yet experienced, to bring about the complete annihilation of the human race.

Not only is the first stage of the Sea Devils' attack successful, their associates in this dastardly plan are the sinister Silurians, also known to the Doctor of old.
 

"These human beings will die as they have lived - in a sea of their own blood!"

The year is 2084, and two power-blocs are poised on the brink of war. Using a series of undersea complexes and deep space sattelites, each bloc carefully monitors the other's movements, slowly edging towards the moment when one will launch an all-out nuclear attack on the other.

Arriving on Sea Base Four, the Doctor, Tegan and Turlough are rapidly drawn into the web of intrigue which enmeshed the era's paranoid political manoeuvrings. Not everyone on board the base is working for the same team, and the officer directly responsible for implimenting the base's nuclear capability has died in mysterious circumstances.

Amid the already tense atmosphere, the crew of Sea Base Four faces an even greater threat to mankind. The Silurians and the Sea Devils, prehistoric reptile men who went into hybernation millions of years before, have reawoken and intend to launch another attempt to reclaim the Earth from humanity. The Doctor must tackle enemy sabotage and face the Myrka, a giant marine monster - but can he prevent the Silurians from implementing their "final solution" - launching the missles to start a war that threatens to wipe out the human race?

Running time: 97 mins approx.

Produced by John Nathan-Turner
Directed by Pennant Roberts
Cover Illustration by Colin Howard