Creepier than any film has a right to be, this American indie chiller has a complete answer to any charge of being manipulative or prurient: the events it depicts really took place.
In fact, a close reading of what actually happened on April 9, 2004 in a McDonald's in Mt Washington, Kentucky, suggests that writer-director Zobel has exercised virtually no creative licence, which is what gives the film a visceral punch.
If you think what follows contains a spoiler, don't worry: you tumble to what's happening early on and the steadily growing horror derives in large part from the fact that every time you say to yourself "he can't do that", the answer is "he did, actually".
Not a film for the faint of heart - study the censor's rating and consider yourself warned - it takes place almost completely in real time in an understaffed, slightly chaotic branch of a fast-food franchise called ChickWich.
An opening sequence of snappy precision - which gives us a brief spoiler of its own - introduces us to the manager, Sandra, who is just keeping things together and trying to ignore the sneering contempt of her teen workforce.