Marcy suffers from Tourette's syndrome and is prone to obsessive-compulsive behaviour, and Seth is an insecure, petty thief. They meet while shoplifting a store in their Upstate New York hometown. Marcy starts to get twitchy about finding a black Barbie styling head, and soon, the pair are off to Toronto in search of one. Alcohol and sex have been Marcy's preferred therapies to control her muscle spasms, but when her condition begins to worsen, Seth suggests that she try the proper medication.

They break into a pharmacy one night and the owner shoots Seth in the leg. On the run, they overturn their car and are helped by a lonely widower Walter until Marcy, becoming more unpredictable, beats him up. They now must run again, this time towards an inevitable tragic end.