Marty McFly and his friend Dr. Emmett "Doc" Brown travel from 1985 to 2015 to prevent Marty's son from sabotaging the McFly family's future. Their arch- nemesis Biff Tannen steals Doc's DeLorean time machine and uses it to alter history for his benefit, forcing the duo to return to 1955 to restore the timeline.

References:
https://en.wikipedia.org/wiki/Back_to_the_Future_Part_II