One night, a couple are traveling on the road. As they are listening to the radio, when breaking news comes on. A patient from the local madhouse has escaped. The couple become filled with fear, so they decide to get to their house as soon as possible.
Unfortunatly, the car is almost out of gas. So they drive under a large oak tree, and they run out of gas. There is a sound in the bushes, and the guy decides to check it out. Before he leaves, he tells the girl to not leave, and three knocks will let her know that that's him. So he leaves.
Time passes, and the girl becomes worried. But she hears three knocks and becomes relieved, but the knocking continues. She becomes terrified, and crawls to the back of the 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, and warn her not to look behind her. But she could not restrain her curiosity and looks behing her. She falls to the ground crying. Her boyfriend is hanging from the tree, and slashed from his neck to his groin. The continous knocking was his feet tapping the roof of the car.