David Mann (Dennis Weaver) departs from his home on a trip. While driving through the desert in his car, he overtakes an 18-wheeled tanker truck. The truck, who's driver we don't see, starts following and tailgating David. First the truck driver seems only to want to irritate David, but before long, the truck gets more aggressive, actively trying to force David into having an accident. In a truck stop, David tries to see who is the driver of the truck, but fails, and is chased once again when he gets back on the road. David tries to hide from the truck, but several attempts are all to no avail. When David's car starts to overheat from a radiator problem, things must come to a head...