The Master wants to steal an ancient, omniscient space race to use it as an engine for his TARDIS
Adric’s dead. Yay! Ahem, sorry… Adric has just died and the remaining TARDIS team are mourning the loss of such a worthwhile companion. Doc thinks they could do with cheering up so puts the TARDIS on track for The Great Exhibition, Hyde Park, London, Earth, 1851. Alas, that little adventure will have to wait because some external force is causing problems for the TARDIS and they have to materialise mid-flight at Heathrow Airport in the present day. Good job too as a Concorde has just gone missing and they’re going to need the help of Doc and his TARDIS to track it down.
Why? Because the plane’s gone through a time contour and ended up 140 million years in the past, that’s why! It would be far too simple to just pop back in time to find it in the TARDIS, so Doc hitches a ride on another Concorde and everyone winds up in a prehistoric land where everything is not quite as it seems. Mysterious psychokinetic forces are at work, and there appears to be someone or something behind them. Good job Nyssa has developed her own extrasensory perception then as they’ll need that to find out who’s masterminding these series of events and get the Concorde crew and passengers safely back to their own time.