Marty McFly is a teenager living in Hill Valley in 1985, where his home life feels bleak: his mother Lorraine is depressed and struggles with alcoholism, his older siblings drift through life without purpose, and his father George is a meek man who is routinely bullied by his supervisor, Biff Tannen. After his band fails a music audition, Marty opens up to his girlfriend, Jennifer Parker about a fear that he might become a mirror of his parents’ failures even as he clings to his own ambitions.
That night, Marty meets his eccentric scientist friend, Doc Brown, in the Twin Pines mall parking lot. Doc unveils a time machine built from a modified DeLorean, powered by plutonium he swindled from Libyan terrorists. The plan is simple in theory: they set a destination for November 5, 1955—the day Doc first conceived his time travel invention. But trouble erupts when the Libyans track them down and gun Doc down. Marty escapes in the DeLorean, and in a flurry of fear and adrenaline, the car rockets to 88 miles per hour and disappears into time.
Marty arrives in 1955 with no plutonium to power a return trip home. As he navigates a younger Hill Valley, he unexpectedly meets his teenage father George and learns that Biff’s influence runs even then. A car nearly hits George while he’s spying on Lorraine, and Marty is knocked unconscious, only to awaken and find Lorraine caring for him and, rather than repelled, becoming infatuated with him. Desperate, Marty tracks down a younger Doc and explains that he is from the future, but Doc warns that the only source capable of generating the 1.21 gigawatts needed for time travel in 1955 is a bolt of lightning. Marty reveals a flyer from the future that details an upcoming lightning strike at the courthouse, and as the worry over his fading siblings grows—one by one, they begin to disappear from a photograph he carries—Doc realizes that Marty’s actions are altering the timeline and could erase his own existence: Lorraine’s affection now leans toward Marty instead of George.
To fix the timeline, Lorraine invites Marty to the high school dance, and he schemes to appear as if he is making a move on her to spur George into acting as a protector. The plan backfires, however, when Biff’s gang locks Marty in the trunk of the band’s car and Biff tries to assault Lorraine. George arrives just in time, defeats Biff, and escorts Lorraine to the dance. The band frees Marty; though his hand is injured, he steps in as lead guitarist, and George and Lorraine share their first kiss, signaling that the future may still be salvageable. With the risk to his own existence now diminished, Marty hurries to the courthouse to meet Doc.
Doc discovers a note from Marty warning him about the consequences of altering the future and rips it up, fearing the potential havoc it could unleash. To save his own life and ensure the proper sequence of events, Marty recalibrates the DeLorean to return ten minutes before he originally left for the future. The lightning strikes, propelling him back to 1985, but the DeLorean falters and he must sprint back to the mall. He arrives just as Doc is being shot. Although Marty mourns briefly, Doc reveals that he had found and reassembled Marty’s note and is wearing a bulletproof vest. Together they return home, and Doc departs in the DeLorean for a journey to 2015. Marty awakens the next morning to a world where his father is now a confident, successful science fiction author, his mother is fit and happy, his siblings are thriving, and Biff is a servile valet in George’s employ. Reunited with Jennifer, Marty begins to grasp the extent of the altered life he now leads. But Doc soon reappears in the DeLorean, urging them to return with him to the future to safeguard their children from looming fates.
