Scotland Yard is hunting the worst kind of serial killer—one with a sense of humor.

When children's book author Oliver Swithin, reluctant creator of the notorious "Finsbury the Ferret," finds an old friend's body floating in a Trafalgar Square fountain, he can't convince the police to treat the death as a murder.

But then more corpses turn up daily—on a tube station platform, in a botanical gardens hothouse, even in the middle of Piccadilly Circus—each murdered in an increasingly bizarre manner. It seems that a serial killer is at play, using London's landscape as his game board.

Oliver joins his uncle, Detective Superintendent Tim Mallard, in a race to uncover the pattern behind the growing number of deaths. But even if they solve the murderer's puzzle, will it help them identify the next victim before the killer strikes again? And will Oliver ever reveal his secret passion for Mallard's assistant, the forbidding Detective Sergeant Effie Strongitharm?

And what does any of this have to do with a battery-operated ferret, the works of Lewis Carroll, the great London Scorpion Scare, the episode of the nude Macbeth, and Underwood Tooth, the world's leading expert on being ignored?