After the time travel adventures of the first movie, Marty McFly is ready to return to a normal life until Doc Brown return in the modified time machine from the year 2015 with a grave warning. Marty, Doc Brown, and Marty's girlfriend Jennifer go back to the future, 2015, to solve to problem facing the McFly family of 2015. While tying up some loose ends Biff of 2015 learns of the time machine and uses it for a trip back to 1955. He gives the younger version of himself a book containing the outcome of sports games in an attempt to gain his past self riches.
Marty, Jennifer, and Doc Brown return to 1985 unaware of Biff's journey and they find that the 1985 they return to is dramatically different than the one they came from. Biff's meddling has altered the time line and Marty and Doc Brown have to go back in time to stop Biff without running into the Marty visiting 1955 from 1985 and not altering events that Marty altered during his first visit to 1955.