To all appearances, Humphrey Boddershaw, the amiable headmaster of Ambrose House Preparatory School for Boys is a man with hardly a care - or an enemy - in the world. How deceptive appearances prove to be when a house party assembles at Ambrose House early in September for a week of croquet matches. One of the guests, Cicely Ravell, makes no secret of the fact that she finds her host to be a violent and wicked man. The local police superintendent reports there is a convict on the loose who has an old score to settle with Humphrey. Then, one night at dinner, Humphrey's own niece threatens to kill him. Still, it gives everyone something of a start when Humphrey Boddershaw is found murdered. And something of a jolt as they begin to realize that someone staying at Ambrose House is quite probably a murderer.