Halfway through the film, the couple picks up a third party, Max, who claims to be under attack.
The director, Jeremy Lovering, famously withheld the script from the actors to create genuine paranoia and confusion.
If the path to your destination requires a mysterious escort who disappears halfway through, turn around immediately while you still have fuel.
The antagonist, Max, eventually reveals himself as the true culprit who has been stalking the couple. Watch for signs of tampering, such as gas cans appearing in your seat or tubes attached to your exhaust pipe.