Initially suspecting sabotage, he soon discovers that the nearby cave system conceals a colony of an ancient race called the Silurians. Awaking from a hibernation which has lasted millions of years, they are now planning to reclaim the Earth from humankind.

The Sea Devils - Arrested after the events at Devils End, the Master has been incarcerated at a top security prison on a remote island off the south coast of England. When the Doctor and Jo Grant pay a visit to their old enemy, they find him a reformed character. But can the spate of mysterious shipping accidents and garbled reports of sea monsters in the local area really be a coincidence? The Doctor soon finds himself pitted against the Sea Devils, an ancient race of reptile intent on eliminating humankind and reclaiming the Earth for themselves.

Warriors Of The Deep - Earth 2084. Two global superpowers hover on the brink of war. When the TARDIS is forced to make an unplanned visit to Sea Base Four, the Doctor, Tegan and Turlough find themselves accused of being enemy agents. Quickly embroiled in a deadly game of paranoid intrigue, it becomes clear that others on the base have sabotage and murder in mind.

However, there is a greater threat to humankind: the Silurians and Sea Devils, prehistoric reptiles seeking to reclaim the Earth. Can the Doctor prevent them from implementing their "final solution" and triggering a war that could wipe out the entire human race?.