One night, a couple is traveling on a country road. As they are listening to the radio, a news flash appears announcing that a patient from the local asylum has escaped. The couple becomes filled with fear, so they decide to get to their house as soon as possible.
Unfortunately, the car is almost out of gas, so they have to drive under a large oak tree to rest for the night. There is a sound in the bushes, so the guy decides to check it out.
Before he leaves, he tells the girl to stay put, and that he'll make three knocks on the roof of the car to let her know that it's him.
Time passes, and the girl becomes worried, but she soon hears three knocks and becomes relieved, but the knocking continues. She becomes terrified, and crawls to the back seat, and stays there until morning. She wakes up to see the police opening the door.
They guide her out and walk her away from the car, warning her not to look behind her. She can not restrain her curiosity and looks behind before falling to the ground crying. Her boyfriend is hanging from the tree, slashed from his neck to his groin. The continuous knocking was caused by his feet tapping the roof of the car.