This fourth mystery novel in which the noted psychiatrist-detective, Dr. Morelle, and his Secretary, Miss Frayle, set out to probe a murder, begins when beautiful Thelma Grayson called at Dr. Morelle's house in Harley Street, and vividly describes how, the night before, she had deliberately shot the notorious Ray Mercury. Mercury, Thelma tells Dr. Morelle, had been directly responsible for her sister's suicide. The morning newspapers have, however, reported that Mercury shot himself. The question she now asks is: should she give herself up to the police, or should they be left to believe that Mercury, who anyway deserved to die, really had committed suicide? Dr. Morelle's search for the answer leads him through a series of dark adventures in Soho's underworld, and involves him and Miss Frayle with a very odd assortment of characters, before he unravels the mystery sur-rounding Mercury's death and finally traps the murderer.