The Doctor and Sarah arrive in 1970s London to find that it has been evacuated, due to the mysterious appearance of dinosaurs. It turns out that the dinosaurs are being brought to London via time machine in order to further a plan to revert London to a pre-technological level.
Doctor Who, the Television Companion quotes a contemporary review that rather unkindly describes the dinosaur special effects thusly: "After escaping they [the Doctor and Sarah] came up against the first dinosaur and, oh dear, shades of Basil Brush! A glove puppet nervously skiing about London streets didn't exactly fill me with fright..."
The story was written by Malcolm Hulke and directed by Paddy Russell. The cast also includes Nicholas Courtney (as the recurring character Brigadier Lethbridge-Stewart), John Levene (Sergeant Benton), Richard Franklin (Captain Yates), Brian Badcoe (Adam), John Bennett (General Finch), Martin Jarvis (Butler), Noel Johnson (Charles Grover MP), Peter Miles (Professor Whitaker), Carmen Silvera (Ruth), and Terence Wilton (Mark).
See also List of Doctor Who serials