Ellen Carson is a real estate agent who inadvertently cuts off a delivery truck driver while changing lanes on the freeway to hurry home. The truck driver turns out to be a disturbed man named Eddie Madden, who proceeds to chase after Ellen in an effort to run her off the road. Ellen in fear calls the 1-800 number on the back of his truck and lodges a complaint, which causes Eddie to lose his job, and he (being a grieving husband and father who earlier lost his family to a car accident) sets out to destroy Ellen's family and soon becomes fixated on Ellen and her teenage stepdaughter Cynthia and plots to have them as replacement family, by removing the head of the house, Ellen's husband and Cynthia's father Jim Carson.