Arriving back on modern-day Earth, the Doctor and Sarah discover London is deserted and under martial law. They eventually find an army patrol, but are arrested as looters and are sent to a detention centre as prisoners. But as their journey begins, their transport comes under attack by a Tyrannosaurus Rex. Dinosaurs have invaded London! UNIT has been called in to assist the army with the running of the city and to try and find a solution to the problem.

Released from captivity, the Doctor takes up his old role of UNIT’s scientific advisor in order to help try and discover why dinosaurs keep appearing and disappearing from London’s streets.

The Doctor suspects a deliberate plan is causing the dinosaur menace, but who is behind the scheme? Who amongst his allies can be trusted? And when Sarah vanishes, just how does she find herself on a spaceship carrying hundreds of people in suspended animation towards a new life on a distant New Earth?