Hen and her husband Lloyd have settled into a quiet life in a new house outside of Boston. But when they meet the neighbors next door, that calm begins to erode. Could her neighbor, Matthew, be a killer? The more Hen observes Matthew, the more she suspects he's planning something. 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.