It's not a bit surprising that this movie is based on a play, since it's rather theatrical: except for a couple of scenes tacked onto the beginning and end, it's a one-set mystery, and a rather gimmicky one at that. What makes it involving, however, is the subtext and Elizabeth Ashley's amazingly sexy performance. The film is really about art of deception and the seduction of play-acting. In one especially weird scene, the ever-bland Franciscus and a white-hot Ashley (those eyes!) almost get busy by poolside. You know at least one character is about to succumb to a lie. Later, the Klug-man has his most believable (and least mannered) moment when he embraces a deception and hollers at Franciscus, "where you come from, are all cops HONEST?" I've never considered Elizabeth Ashley a babe -- then again, most of what I've seen her do are lame made-fors and cheesy thrillers. But she won a Tony nomination for playing Maggie in "Cat on a Hot Tin Roof" so maybe she saved all her sensuality for these two roles.
