Twenty-year-old Dane Calloway is alone for the summer when an unmarked box lands on his doorstep: a black sleeve, no sender, and a card with three lines - coat it with something that belongs to her, strap it on, and she will feel it. The her is Margot Deluca, twenty-eight, the florist two doors down, engaged to a contractor six weeks away on a job site. Dane tells himself it is a prank. That night Margot wakes with no one in her room and no mark on her body. She books a doctor's appointment; Dane starts watching her windows. Grant comes home, then leaves again, and asks the kid next door to keep an eye on her. Margot works out that it only happens when she is alone - and stops the moment Dane is in the room. Neither of them says a word. Then a second package arrives, and a third, and Dane realises the thing was never really aimed at her. Someone has been watching them both, and someone else has already paid for it.
