“I had reached the middle of my life and knew less than I ever had before,” writes Dani Shapiro in her quietly searing memoir, Devotion (Harper, $25). Shapiro can easily tick off all that is right in her life: loving husband, healthy child, charming old house in Connecticut, work that both sustains and rewards. But inside, she is falling apart. At night, she “quivered in the darkness like a wounded animal.” She knew that “something was very wrong,” but could not locate source of the trouble.