Somewhat diverting puzzle from an old pro (Fall From Grace, etc.). The self-sacrificing heroine this time is Margaret Berringer, whose life outside work is devoted mostly to bitter, self-pitying brother David, a paraplegic. Injured while inspecting his half-finished Long Island house, David blames architect Sandy Fleming and now, a year later, is threatening to kill him. When Sandy is then found shot to death at the house site. Margaret is driven to clear David in her own mind, even though the police can't make a case against him. Sandy's dim widow Myra, his partner Ken Ash, current girlfriend in Chicago, lawyer brother Simon, high-school friend Leslie Sommers--even his taciturn housekeeper Helene--all are subjected to Margaret's intense questioning and scrutiny, intensified when Myra becomes a second victim. The crucial clue comes early and the alert reader won't have too much trouble figuring out the scenario. The dull reports from Margaret's stream of consciousness tend to slow the action, but this is still one of the author's better efforts.