Commander Sam Vimes of the City Watch is used to trouble. There's always trouble in Ankh-Morpork.

But this is new: people are being brutally murdered and there's no evidence of anything alive having been at the crime scene. At the same time, the most powerful man in the city has been poisoned and is clinging on to life by a thread.

It's a conundrum of a case. With the help of Captain Carrot, the only watchman who knows the law inside-out; Corporal Cheery Littlebottom, an unconventional dwarf with an eye for forensics; and Constable Angua, a werewolf with an excellent sense of smell, Vimes tries to solve the mystery.

But time is of the essence, for something extremely dangerous is loose in the city, its red eyes glowing in the night ...

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