In this twentieth volume in Perry's best-seller William Monk series set in Victorian England, Perry has focused on a situation that will resonate with modern readers: a terrorist attack resulting in the deaths of innocent bystanders. In this instance, Monk, the Commander of the Thames River Police, is an eye witness when a bomb blows up a riverboat pleasure cruise, killing two hundred men, women and children injured by the explosion or trapped in the sinking boat, or drowned in the darkness and confusion despite desperate efforts to rescue survivors. Just before the explosion, Monk himself witnessed a man jump off the ship and saw the man being picked up by a small craft waiting nearby.
Monk and his men have already begun to investigate this lead when he is abruptly informed that because the bombing has political implications, the investigation is being taken over by the Metropolitan Police. It seems this is justified when the new investigators quickly make an arrest: an Egyptian immigrant with an unsavory past and a known grudge against the British occupation of Egypt. The man is quickly tried, found guilty and sentenced to be hanged.
But when Monk uncovers evidence, while pursuing another case, that shows that the convicted man was somewhere else when the boat exploded, he knows that others must be involved in the crime. The man in prison might have been an accomplice, perhaps was set up to be the scapegoat, but was not the one who placed the bomb and lit the fuse.
With the help of his wife, Hester, with her invaluable contacts in society both high and low; their adopted son, Scuff, with his own intimate knowledge of the River; and their friend the disgraced barrister Sir Oliver Rathbone; Monk doggedly pursues the truth that unknown powerful interests are desperate to obscure, putting at risk not just his own life but Hester's life as well.
