Graham and Joan Bendix have apparently succeeded in making that eighth wonder of the modern world, a happy marriage. And into the middle of it there drops, like a clap of thunder, a box of chocolates. Joan Bendix is killed by a poisoned box of liqueur chocolates that cannot have been intended for her to eat. The police investigation rapidly reaches a dead end. Chief Inspector Moresby calls on Roger Sheringham and his Crimes Circle six amateur but intrepid detectives to consider the case. The evidence is laid before the Circle and the members take it in turn to offer a solution. Each is more convincing than the last, slowly filling in the pieces of the puzzle, until the dazzling conclusion.