Still coping from the loss of their parents, Malcolm and Isabel Rademacher head to their family's lake house for a weekend. What starts as a fun trip is cut short when two masked assailants invade their home. Malcolm kills one of the men in order to save his sister but, when the second invader flees the scene, he becomes obsessed with tracking him down. Isabel becomes aware of the darkness that her brother carries inside and, while he claims to be protecting her, she worries that he may be the biggest threat of all.