When an old flame of Burke's is gunned down, he uncovers the darker side of her relationship with several men. The former chauffeur for the victim's father, an old friend of the family, an philandering astronomer and his embittered wife, a free-wheeling B-girl, a vulgar jazz trumpeter - any one could have killed ""my girl"". The truth may lie in Diana's little black book. Les and Tim are worried that Burke is too close to the case to handle it rationally. Burke refuses their help. Only after he is attacked in his own home and, later, is forced to hear the truth about Diana's past, does Burke realize who the killer is, with the help of Les's wristwatch.