In the Bill Kirby Murder Case, Richard Diamond, a private detective, is approached by Mrs. Lenore Kirby, who is worried about her son, Bill. Bill, also a private eye, has been acting strangely, becoming increasingly irritable and secretive. After a series of troubling events, including a large sum of money found in his belongings, Bill disappears, prompting his mother to seek Diamond's help. She reveals that Bill had been sending her more money than usual, which raises further questions about his activities.