Three Legs in the Evening comes from the Sphinx's riddle in Sophocles' Oedipus Rex, in which Oedipus is asked what creature walks on all fours in the morning, on two legs in the afternoon, and three in the evening. The answer, which Oedipus gets right, is Man, who crawls as a baby, walks upright as a man, and leans on a cane in his old age. Received wisdom, in other words, can be unreliable. Enter the story of Sally B, an over-sixty widow about...