Set in Rome and Britannia in AD 75, the novel stars Marcus Didius Falco, informer and imperial agent.

The title refers to the discovery of a corpse hidden beneath the floor of one bath house and a murder which takes place in another.

When Marcus Didius Falco discovers a corpse hidden under the floor of his new bath house, he starts to track down the men responsible – Glaucus and Cotta.

Suspecting that the men he seeks have fled to Britain, Falco accepts the mission and travels there with his wife, two baby daughters, their nurse, and his two brothers-in-law Aelianus and Justinus.

However events quickly take a turn for the worse when the Chief Architect is found murdered in the bath-house of the British King.