

The Doctor and Jo visit the Master in his high-security prison on an island off the south coast of England. The governor, Colonel Trenchard, says ships have been disappearing mysteriously at sea. The Doctor discovers that Trenchard and the Master are in league to contact the Sea Devils, a race of reptiles in hibernation in a base beneath the sea, who have been awoken by recent work on a nearby sea fort. The Master intends to use his new allies to help him conquer the world!
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Cast

Jon Pertwee
The Doctor

Roger Delgado
The Master

Katy Manning
Jo Grant

Edwin Richfield
Captain Hart

Clive Morton
Trenchard
June Murphy
3rd Officer Jane Blythe

Donald Sumpter
Commander Ridgeway
David Griffin
Lt. Commander Mitchell
Hugh Futcher
Hickman

Royston Tickner
Robbins

Pat Gorman
Sea Devil

Peter Forbes-Robertson
Chief Sea Devil
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