Doctor Who And The Dinosaur Invasion

The Doctor walked slowly forward into the cul-de-sac. The giant dinosaur turned its head to focus on the midget now approaching - the Doctor aimed his gun to fire - suddenly from behind came a great roar of anger. He spun round - blocking the exit from the narrow street towered a Tyrannosaurus rex, its savage jaws dripping with blood ...

The Doctor and Sarah arrive back in the TARDIS to find London completely deserted - except for the dinosaurs. Has the return of these prehistoric creatures been deliberately planned and, if so, who can be behind it all?