In the title story, a young matron from a convalescent home is found dead in a quiet Maida Vale street. The Daily Telegraph ran an article headed 'Murder or Suicide?' on the subject of the mysterious death. In The Hocussing of Cigarette an earl's racehorse is the victim of attempted poisoning. Who Stole the Black Diamonds? concerns a mystery that bewilders police and diplomats across Europe. All of the twelve detective stories in this volume are puzzled over by Orczy's mysterious armchair detective, the old man in the corner.