Source plot synopsis — includes the ending
On October 26, 1985, Dr. Emmett "Doc" Brown arrives unexpectedly in the DeLorean time machine, persuading Marty McFly and his girlfriend, Jennifer Parker, to travel to the future with him and help their future children. Once they arrive in 2015, Doc incapacitates Jennifer, leaving her asleep in an alley to avoid letting her learn about her own future. Doc explains that their son Marty Jr. will be arrested for participating in a robbery with Biff Tannen's grandson Griff, leading to a chain of events that destroys the McFly family.
Doc instructs Marty to switch places with the identical Marty Jr. and refuse Griff's offer, but Griff goads Marty into a fight by calling him "chicken", and a hoverboard chase ensues. Griff and his gang are arrested, saving Marty's future children. Before rejoining Doc, Marty purchases an almanac containing the results of major sporting events from 1950 to 2000. Doc discovers it and warns Marty about profiting from time travel. Before Doc can adequately dispose of it, they are interrupted by the police, who have found Jennifer incapacitated and are taking her to her 2015 home. They pursue, as does an elderly Biff, who has overheard their conversation and retrieved the discarded almanac.
Jennifer wakes up in her 2015 home and hides from the McFly family. She overhears that her future life with Marty is not what she expected, due to his involvement in an automobile accident, and witnesses Marty being goaded by his co-worker, Douglas Needles, into a shady business deal, resulting in his firing. Jennifer tries to escape the house but faints after encountering her future self. Meanwhile, unbeknownst to Marty and Doc, Biff steals the time machine and returns it. Marty and Doc return to 1985, leaving an unconscious Jennifer on her front porch to sleep off the day's events as a dream.
Marty gradually realizes that the 1985 they have returned to is not the one he knows. Biff, having used the almanac to secure a fortune, is now one of the country's wealthiest and most corrupt men. He has turned Hill Valley into a chaotic dystopia with a casino hotel, secretly killed Marty's father, George, in 1973, forced Marty's mother Lorraine to marry him, and sent Marty to boarding school in Switzerland. Meanwhile, this timeline's version of Doc has been committed to a mental hospital. Doc deduces that old Biff took the time machine to give his younger self the almanac, and Marty learns from the alternate 1985 Biff that he received it on November 12, 1955, the date Marty had recently visited. Biff, acting on his future self's advice, tries to kill Marty, who flees with Doc to 1955.
Marty secretly follows the 1955 Biff and watches him receive the almanac from his 2015 self. Marty then follows him to the high school dance, carefully avoiding interrupting the events from his previous visit, and being forced to intervene when Biff's gang goes after the other Marty performing onstage. Marty finally gets the almanac but loses it after being again goaded into a fight with Biff. Marty chases after Biff's car on the hoverboard, getting the almanac back as Biff is left to crash into a manure truck for the second time in a week.
Marty burns the almanac, nullifying the changes to the timeline that it had caused, as Doc hovers above in the time machine. Before Marty can join him, the DeLorean is struck by lightning and disappears, leaving Marty once again stranded in 1955. A Western Union courier arrives and delivers a letter to Marty from Doc, who tells him that the lightning strike transported him to 1885. Marty races back into town to find the 1955 Doc, who had just helped the other Marty to return to 1985. Shocked by Marty's sudden reappearance and that he is "back from the future", Doc faints.
Doc instructs Marty to switch places with the identical Marty Jr. and refuse Griff's offer, but Griff goads Marty into a fight by calling him "chicken", and a hoverboard chase ensues. Griff and his gang are arrested, saving Marty's future children. Before rejoining Doc, Marty purchases an almanac containing the results of major sporting events from 1950 to 2000. Doc discovers it and warns Marty about profiting from time travel. Before Doc can adequately dispose of it, they are interrupted by the police, who have found Jennifer incapacitated and are taking her to her 2015 home. They pursue, as does an elderly Biff, who has overheard their conversation and retrieved the discarded almanac.
Jennifer wakes up in her 2015 home and hides from the McFly family. She overhears that her future life with Marty is not what she expected, due to his involvement in an automobile accident, and witnesses Marty being goaded by his co-worker, Douglas Needles, into a shady business deal, resulting in his firing. Jennifer tries to escape the house but faints after encountering her future self. Meanwhile, unbeknownst to Marty and Doc, Biff steals the time machine and returns it. Marty and Doc return to 1985, leaving an unconscious Jennifer on her front porch to sleep off the day's events as a dream.
Marty gradually realizes that the 1985 they have returned to is not the one he knows. Biff, having used the almanac to secure a fortune, is now one of the country's wealthiest and most corrupt men. He has turned Hill Valley into a chaotic dystopia with a casino hotel, secretly killed Marty's father, George, in 1973, forced Marty's mother Lorraine to marry him, and sent Marty to boarding school in Switzerland. Meanwhile, this timeline's version of Doc has been committed to a mental hospital. Doc deduces that old Biff took the time machine to give his younger self the almanac, and Marty learns from the alternate 1985 Biff that he received it on November 12, 1955, the date Marty had recently visited. Biff, acting on his future self's advice, tries to kill Marty, who flees with Doc to 1955.
Marty secretly follows the 1955 Biff and watches him receive the almanac from his 2015 self. Marty then follows him to the high school dance, carefully avoiding interrupting the events from his previous visit, and being forced to intervene when Biff's gang goes after the other Marty performing onstage. Marty finally gets the almanac but loses it after being again goaded into a fight with Biff. Marty chases after Biff's car on the hoverboard, getting the almanac back as Biff is left to crash into a manure truck for the second time in a week.
Marty burns the almanac, nullifying the changes to the timeline that it had caused, as Doc hovers above in the time machine. Before Marty can join him, the DeLorean is struck by lightning and disappears, leaving Marty once again stranded in 1955. A Western Union courier arrives and delivers a letter to Marty from Doc, who tells him that the lightning strike transported him to 1885. Marty races back into town to find the 1955 Doc, who had just helped the other Marty to return to 1985. Shocked by Marty's sudden reappearance and that he is "back from the future", Doc faints.
Sources and content license
Source and revision history ↗ · Adapted from Wikipedia contributors, Back to the Future Part II. Section headings and formatting adjusted. · Content license