The movie is about a 12-year-old schoolboy named Trevor who is given a class project to complete by his social studies teacher Mr. Simonet. His task is to come up with a plan thatwill change the world but doing it himself. On his way home from school later that day, Trevor notices a homeless man, Jerry and decides to make a difference in Jerry's life.
Trevor then comes up withthe plan to "pay it forward" by doing a good thing for three people who must do good things for three other people, each creating a charitable pyramid scheme.
The next morning, Trevor's mother,Arlene, a single mother recovering from alcoholism, becomes angry with Trevor after finding Jerry in their garage fixing her truck. She goes to school and confronts Eugene because of his task Trevor hasallowed Jerry into their home. But Eugene is also intrigued by Trevor's response to the social studies project.
Later that night back at their home, Trevor confronts his mother about her alcoholism, andin a fit of anger she hits him in the face. Trevor runs away from home, and Arlene asks Eugene to help her find him. They find Trevor at a bus station, about to be molested. Eugene rescues him andArlene apologizes with Trevor.
Chris, a journalist, is trying to find out why a total stranger gave him a brand new Jaguar car after Chris' old Mustang was damaged in a car accident. The stranger'sonly explanation is that he is simply "paying it forward". When Chris asks him for more information, the man explains that, when he recently visited a hospital while his daughter was suffering an asthmaattack, a gang member suffering from a stab wound actually took up a gun to force the doctors to look at the man's daughter before she collapsed, prompting Chris to begin his search again.
AfterTrevor's apparently unsuccessful attempt to help Jerry, he decides to help Eugene by setting him up with Arlene, Trevor's own mother. Their relationship grows in strength until Arlene's ex-husband,...