After his father's accidental death, Kale (Shia LaBeouf) becomes sullen, withdrawn and troubled. When he lashes out at a well-intentioned but insensitive teacher, he finds himself under a court-ordered house arrest. His mother, Julie (Carrie-Anne Moss), works night and day in order to support herself and her son, as she tries in vain to understand the changes in his personality.

The walls of his house begin to close in on Kale as he takes chances to extend the boundaries of his confinement. His interests turn outside the windows of his suburban home toward those of his neighbours, including a mutual attraction to the new girl next door (Sarah Roemer). Together, they begin to suspect that another neighbour is a serial killer. Are their suspicions merely the product of Kale's cabin fever and vivid imagination? Or have they unwittingly stumbled across a crime that could cost them their lives?