At a costume party with the dubious theme of 'famous murderers and their victims', the know-it-all amateur criminologist Roger Sheringham is settled in for an evening of beer, small talk and analysing his companions. One guest in particular has caught his attention for her theatrics, and his theory that she might have several enemies among the partygoers proves true when she is found hanging from the 'decorative' gallows on the roof terrace. Noticing a key detail which could implicate a friend in the crime, Sheringham decides to meddle with the scene and unwittingly casts himself into jeopardy as the uncommonly thorough police investigation circles closer and closer to the truth. Tightly paced and cleverly defying the conventions of the classic detective story, this 1933 novel remains a milestone of the inverted mystery subgenre.