Between the murder of frail Mr.Takahashi, who owned the greenhouse near Betty Trenka's home, and the stroke that incapacitates her retired boss Sid, Betty's not in the best of spirits. So when Sid Junior asks her to clear out his father's files, she starts packing, glad to be able to help Sid Senior, the only man she's ever loved. But the feeling of unease that pervades the office is unnerving. Betty can't help wondering why people are so interested in her little assignment. Perhaps the crammed files will provide the key - under M for murder.