The Doctor's time-travelling machine is trapped in the flight-path of an alien spacecraft in orbit around the Earth. To avoid the fatal impact of a head-on collision the TARDIS resorts to the only escape possible and materialises on board the on-coming liner.

This solves the immediate problem, but a new difficulty arises - the TARDIS cannot get off the ship until a radio signal transmitting from Earth has been disconnected.

The Doctor sets off in a Transmat Capsule, having programmed the TARDIS to enable Tegan and Nyssa to follow him once he has dealt with the interference.

Naturally enough, things don't go quite as planned...

The Doctor is enjoying the sun on a holiday island - but things are soon hotter than he bargained for. The young American Perpugilliam Brown brings to the TARDIS a mysterious object that her archaeologist step-father has found in a sunken wreck. Kamelion, the Doctor's robot friend of a thousand disguises, reacts to the object totally unexpectedly, with bewildering consequences for the TARDIS crew. For Kamelion sends the Doctor and his friends to Sarn, a terrifyingly beautiful planet of fire. This strange world provides the key to Turlough's secret past - and once again the Doctor is pitted against the wily Master.

The Doctor and his companions arrive on Tegan's home planet at a moment of crisis: a Concorde aeroplane has inexplicably vanished while in flight.

The Doctor, Tegan and Nyssa, together with the TARDIS, join the crew of a second Concorde that sets out to simulate the fateful journey of the missing supersonic jet...

Coming back to Earth is not the return to normality that the rescue team might reasonably have expected. Seeing is believing, people say. The Doctor and his friends begin to realise that it just isn't as simple as that...