September 1799. William Pitt is attempting to force through anti-slavery legislation, but many have a vested interest in preventing this change and would go to dangerous lengths to stop it. Meanwhile, Tom Pascoe of the river police is grieving for the woman he loved and looking for solace at the bottom of a bottle. Tom's drinking has made him increasingly belligerent and unpredictable, so when he is called to investigate a body found in the Thames - that of an MP and a close associate of William Pitt - there's doubt whether he's up to the task. But Tom must pull himself together, or be dragged under; Pitt's life is in his hands.

River Surveyor Tom Pascoe of the Marine Police finds the bodies of two men entombed in the crew cabin of a sunken lugger. Suspicion falls on a third member of the crew seen fleeing the scene. He had a known motive for murder. Against the background of a nation at war with Napoleon, Tom Pascoe finds his own life under threat as he digs deeper into the case. He uncovers the existence of French agents whose task is to undermine England's ability to continue the war. Tom's job is further complicated by the presence of a new member of the police crew with a shocking secret of his own...