Returning to London, the Doctor and Sarah Jane find a city almost completely devoid of life. The civilian population has been evacuated in the wake of an unimaginable event: somehow dinosaurs have returned to terrorize the Earth. As the Brigadier and UNIT fend off increasingly vicious attacks from gigantic prehistoric reptiles, the Doctor investigates just how these monsters are appearing without warning. But when Sarah Jane is kidnapped, the Doctor realizes perhaps even his oldest friends can't be trusted. Who is responsible for the devastating carnage? And what will Sarah Jane do when she awakes aboard a spaceship many light years from home?