The third incarnation of the Doctor and his allies try to cope with dinosaurs randomly appearing all across London. If they can't solve this mystery, England, and the world, could be sent back to the stone age. This is not a bad story; it may even be one of the better ones from the period. My biggest problem is that the book tries to mix up the different incarnations of the Doctor too much.
The TARDIS returns the Doctor and Sarah to London, which is strangely deserted. Trying to stop some looters, they are arrested by soldiers who are part of the force policing martial law. They do not know why London is abandoned, but escaping from captivity, but soon come face-to-face with a Tyrannosaurus Rex.
Where did this (and other) dinosaurs come from? Who is behind the return of these mindless creatures?