Inspector Alleyn's wife, the artist Agatha Troy, has a special fondness for Constables-the paintings, that is, not the policemen. So she jumps at the chance to take a river cruise through "Constable Country" in the east of England, in honor of the nineteenth-century master of landscapes. Her enthusiasm dims a little, though, when it becomes clear that the ticket became available at the last minute only because a previous passenger was murdered in his cabin ...