Investigating mysterious power failures and a death at an underground research centre, The Doctor discovers a colony of Silurians - prehistoric, intelligent reptiles who went into hibernation before man evolved. But now they have woken up, and they are prepared to wipe out mankind with a killer plague to get their planet back.
| Writing | Malcolm Hulke | Writer |
| Directing | Timothy Combe | Director |
| Production | Barry Letts | Producer |