Doctor Who And The Silurians: Summoned by the Brigadier to an underground research centre at Wenley Moor, the Doctor and Liz Shaw learn from its director, Dr Lawrence, that work on a new type of nuclear reactor is being hampered by inexplicable power losses and by an unusually high incidence of stress-related illness amongst staff. Investigating a nearby cave system, the Doctor discovers it is the base of a group of intelligent reptiles, termed Silurians, who went into hibernation millions of years ago but have now been revived by power from the research centre. The Doctor strives for peace between reptiles and humans and manages to gain the trust of the old Silurian leader, but then a rebellious young Silurian seizes power and releases a deadly virus that threatens to wipe out humanity. The Doctor finds an antidote, but the Silurians retaliate by taking over the research centre and preparing to destroy the Van Allen Belt, a natural barrier shielding the Earth from solar radiation harmful to humans but beneficial to reptiles...

The Sea Devils: The Doctor and Jo visit the Master in his high-security prison on an island off the south coast of England and hear from the governor, Colonel Trenchard, that ships have been mysteriously disappearing at sea. Investigating, the Doctor learns from Captain Hart, commander of a nearby Naval base, that the sinkings have centred around an abandoned sea fort. He and Jo then visit the fort and are attacked by what one of the men there terms a Sea Devil - an amphibious breed of the prehistoric creatures encountered by the Doctor shortly after his exile to Earth.
The Master, aided by a misguided Trenchard, is stealing equipment from the Naval base in order to build a machine to revive the Sea Devils from hibernation. The Doctor takes a diving bell down to the Sea Devils' underwater base to try to encourage peace...

Warriors Of The Deep: The Doctor, Tegan and Turlough arrive at an underwater Sea Base on Earth, where a scientific and military team led by Commander Vorshak are monitoring a rival power bloc. The team undergo regular missile launch test sequences to ensure that they are ready at all times to combat an attack. Three Silurians led by Icthar - the surviving member of a Silurian triad - revive a colony of Sea Devil Warriors in order to invade the base and use its weapons to attack the opposing power bloc, thus provoking a global war that will allow the reptiles to conquer the Earth...