Agatha Troy (the artist wife of Inspector Alleyn) has a special fondness for Constable's work, so she jumps at the chance to take a river-cruise through Constable country in the east of England. Her enthusiasm dims a little when it becomes clear that the ticket became available at the last minute only because a previous passenger was murdered, it seems, by a notorious international criminal known as the Jampot. The murder's don't stop there - and Troy finds herself caught in the middle of an international criminal ring - setting up a major art forging operation.