When young Mr. and Mrs. Dane return from their honeymoon they find, buried under the cellar floor of the suburban villa they have taken, the body of an unknown girl. Scotland Yard is called in, and finds itself confronted first of all by an almost impossible problem in identification. By an ingenious idea, Chief Inspector Moresby solves the preliminary puzzle, and calls upon his friend Roger Sheringham, to say that the girl was last heard of at a preparatory school where Roger had been deputising, just before her death, as a master. Roger had noticed that there were some strange undercurrents among the staff of the school, and on leaving it had begun a book about the members of it. This manuscript he now hands over to Moresby, and it is given to the reader, who at this stage has not been told the identity of the murdered girl. The action is thus switched back to a fortnight or so before the girl's death, with the result that the reader is given a puzzle new to detective fiction: not, spot the criminal, but, spot the future victim.