When her 25-year marriage suddenly falls apart, journalist Florence Williams expects the loss to hurt. But when she starts feeling physically sick, losing weight and sleep, she sets out in pursuit of rational explanation. She travels to the frontiers of the science of “social pain” to learn why heartbreak hurts so much --- and why so much of the conventional wisdom about it is wrong. Soon Williams finds herself on a surprising path that leads her from neurogenomic research laboratories to trying MDMA in a Portland therapist’s living room, from divorce workshops to the mountains and rivers that restore her. She tests her blood for genetic markers of grief, undergoes electrical shocks while looking at pictures of her ex, and discovers that our immune cells listen to loneliness.