While investigating a vanishing Concorde at Heathrow Airport, the Doctor and his companions are thrown millions of years back in time, when a mysterious alien called Kalid is trying to control the ancient powers of the Xeraphin.

Harry Webster (David Lyon) is an apparently normal husband and father who resides in contemporary Nottingham, England, which was once host to a flourishing textile industry. One day, Harry leaves his house and vanishes. A note he left behind alludes to a double life he no longer wishes to lead. His wife Liz (Annette Crosbie) conducts a search for her husband. Her findings raise a disturbing question: Did Harry have anything to do with a series of recent factory bombings?