Mr. Roger Ferrison has just returned to London after several years of living rough in Canada. He takes a small room in the boarding house run by Mrs. Dewar. There he meets the bewitching invalid Fiona Quayne who rapidly develops a consuming passion for Ferrison. Meanwhile, back at the Boarding House, Colonel Dennett is murdered. One suspects from the very beginning that not all of the boarders at Mrs. Dewar's establishment in Palace Crescent are what they appear to be, and Mr. Oppenheim does not attempt to hide for long the existence of some secret and probably criminal bond between Mrs. Dewar and some of her boarders. The sensational theft of a Jewelry collection, missing Indian rubies, and the lackadaisical intervention of Scotland Yard all contribute to the plot.