Picking up the story where Back to the Future left off the morning of October 26, 1985, Marty McFly and Doc Brown leave Marty's house and time travel to the year 2015 to stop Marty's kids from destroying their lives. Since Jennifer has seen the DeLorean time machine and Doc decides that the matter concerns her as well, they take her along and depart. However, Biff Tannen comes out of the house, intending to show Marty one of the new Biff's Auto Detailing matchbooks he has had printed, and accidentally witnesses their departure. They arrive on a skyway on October 21, 2015, where Doc is forced to tranquilize Jennifer because she asks too many questions about the future; Doc's firm belief is that no one should be allowed to know too much about their own destiny or future.
Doc lands the DeLorean in an alleyway adjacent to the Courthouse Square. Doc and Marty take Jennifer out of the DeLorean and lay her to the side as she is still sleeping and as to not get in the way of the mission. Doc then explains the chain of events that led to the McFlys' downfall and tells Marty the plan on how they will stop it from happening. Originally, Marty Junior is approached by Griff Tannen, Biff's grandson, and his gang and is asked to join in a robbery. The robbery is foiled and Marty Jr. takes the fall. His sister Marlene McFly will later attempt to break him out of jail, only to cause further acrimony for the McFly family. Doc's plan is for Marty to impersonate his son and to tell Griff he will not join in. Marty follows the plan, even though it is almost messed up when Marty Jr. unexpectedly comes into the Cafe 80's. The gang gets angry and chases after Marty, much like the chase in 1955 involving Biff.
Returning to 1985, Marty and Doc leave Jennifer on her porch swing. The first indication that something might be wrong is that there are security bars on the windows of the house. When Doc drives Marty back to his house, it is dark, leaving them unable to notice that the signs at the entrance to Lyon Estates have been defaced, or a pack of stray dogs roaming freely. He is unable to enter his house through the backyard because the gate is padlocked. Crawling through his bedroom window, he is shocked when he discovers that an African-Amercian family lives here as the girl who is in Marty's room screams "Rape!" and her father furiously chases Marty out of the house with a baseball bat.