Hen and her husband, Lloyd, have settled into a quiet life in a new house outside of Boston. Hen (short for Henrietta) is an illustrator and works out of a studio nearby, and has found the right meds to control her bipolar disorder. Finally, she's found some stability and peace. But when they meet the neighbors next door, that calm begins to erode as she spots a familiar object displayed on the husband's office shelf. The sports trophy looks exactly like one that went missing from the home of a young man who was killed two years ago. Hen knows because she's long had a fascination with this unsolved murder - an obsession she doesn't talk about anymore, but can't fully shake either. Could her neighbor, Matthew, be a killer? Or is this the beginning of another psychotic episode like the one she suffered back in college, when she became so consumed with proving a fellow student guilty that she ended up hurting a classmate? The more Hen observes Matthew, the more she suspects he's planning something truly terrifying. Yet no one will believe her. Then one night, when she comes face to face with Matthew in a dark parking lot, she realizes that he knows she's been watching him, that she's really on to him. And that this is the beginning of a horrifying nightmare she may not live to escape ...