On a warm June evening in the village of Didford Magna, four businessmen who share the fishing rights to a prized stretch of the River Didder gather at the Polworthy Arms to compare the day's catches. But beneath the placid surface of chalk streams and mayfly hatches run darker currents: old grudges, secret attachments, and a bitter dispute over a sawmill that has spoiled the best beat on the water. When the season's tensions boil over into violence, the discovery of a body transforms the anglers' paradise into a scene of suspicion.
Local inquiries lead nowhere, and soon a Scotland Yard inspector is called in to untangle a web of alibis, lies, and carefully guarded private papers. Every member of the syndicate seems to have something to hide, from the elderly naturalist with a passion for tree-creepers to the young man hopelessly in love with another man's wife. As the inspector works his way through the riverbank and the village, he must decide whether the murderer was one of the anglers or someone closer to home.