'In the first few months after Charlie died, I began hearing from her much more frequently . . .' When Helen Clapp gets a missed call from best friend Charlie, she knows it's a mistake. Because Charlie's dead. Ghosts break so many fundamental laws of the universe that Helen, a physicist, shouldn't believe in them. Should she? As this question draws Helen to Charlie's grieving husband and daughter, she finds herself entangled in the forgotten threads of lost friendship and her own paths not taken . . .