Time Signatures

Back to the Future Part II is a 1989 film and a sequel to the 1985 film Back to the Future. Like the previous film, it was directed by Robert Zemeckis and written by Zemeckis and Bob Gale. Part II and the third installment of the trilogy, Back to the Future Part III, were filmed back-to-back, with some of the scenes of Parts II and III filmed concurrently, and released six months apart. Although released in 1989 and 1990, both films continued to portray 1985 as the present, due to them directly following the events of the first film.

Part II follows the continued adventures of Marty McFly and “Doc” Emmett Brown as they use their time-traveling DeLorean to travel into a retro-futuristic version of 2015, an alternative 1985 and the principal setting of the first film in 1955. The film ends with a cliffhanger that is resolved in Part III.
Plot
Continuing from the end of Back to the Future, “Doc” Brown (Lloyd) arrives in 1985 from the future and tells Marty McFly (Fox) and his girlfriend Jennifer Parker (Elisabeth Shue) that he needs their help to save their kids in the future. They depart in the flying DeLorean time machine as Biff Tannen (Thomas F. Wilson) witnesses the departure. In 2015, Doc electronically hypnotizes Jennifer and leaves her in an alley to keep her away from his plan. Meanwhile, Doc has Marty pose as his son, Marty McFly, Jr., to refuse a deal from Biff’s grandson, Griff Tannen, which would result in the arrest of Marty Jr. and his sister Marlene. Marty refuses the deal, but Griff goads Marty into a fight; Marty escapes the fight and leads Griff and his gang on a hoverboard race across the courtyard square, ultimately resulting in Griff and his gang crashing through the courtyard windows and changing the future history. On his way back to meet with Doc, Marty purchases an almanac detailing results from major sporting events of the last half of the 20th century. Doc discovers the purchase and accuses Marty of trying to profit from time travel, but before Doc can dispose of the sports book, they are forced to follow the police who have found Jennifer and are taking her to her future home. Old Biff, overhearing the conversation and recalling the DeLorean from 1985, follows with the discarded book.

Jennifer wakes up in her future home and hides while the collected McFly family has dinner together. She overhears that Marty’s life, as well as their life together, is less than they expected due to a car accident that Marty got in many years prior, after being challenged by his friend Needles. As she watches, older Marty is goaded in a shady business deal by Needles and is immediately fired from his job, as announced by numerous faxes (one copy which Jennifer keeps). While escaping the house, Jennifer meets her older self and faints; as Doc and Marty run to retrieve the younger Jennifer, Old Biff steals the DeLorean, travels time, and returns. Doc, Marty, and Jennifer return to 1985, unaware of Biff’s actions, and leave Jennifer on the porch at her home.

Doc and Marty soon discover that this 1985 has changed dramatically, as Biff Tannen has become incredibly wealthy and converted Hill Valley into his own personal paradise. Biff has killed Marty’s father, George, and has forced his mother Lorraine to marry him; Doc has been committed to an insane asylum. Doc finds evidence of the sports almanac and Biff’s trip to the past in the DeLorean, and tells Marty he needs to learn when younger Biff received the almanac so they can go back and correct the timeline. Marty confronts Biff regarding the almanac; Biff explains that he received the book from an old guy on November 12, 1955, the same day as the lightning storm that struck the clock tower and the “Enchantment Under the Sea” dance. Biff also reveals that the old man told him to watch for Marty or Doc looking for the book, and attempts to kill Marty. Doc is able to save Marty, and with new information, the two return to 1955.

Marty works undercover to trail Biff; he is present when Old Biff arrives to give Biff the book, but is unable to retrieve it. Marty is forced, with Doc’s help, to try to get the book back during the dance, being careful to avoid undoing the events that he had already corrected in his previous trip. Eventually, Biff leaves the dance, and Doc and Marty follow him silently, Marty using the hoverboard while tethered to the flying DeLorean by a string of banners. Marty distracts Biff long enough to grab the book, causing Biff to, yet again, crash into a truckload of manure.

With the storm approaching, Doc is unable to set down the DeLorean, and instructs Marty over walkie-talkies to burn the almanac. Upon doing so, their evidence from 1985 returns to what they expect, and all appears to be well. However, as Marty watches, the DeLorean is struck by lightning and disappears. Nearly immediately afterwards, a courier from Western Union arrives and gives Marty a 70-year old letter; Marty discovers the letter is from Doc, who ended up in 1885 after the lightning strike. Marty races back into town and finds the 1955 version of Doc, celebrating the success of having sent the earlier version of Marty back to 1985, and is shocked and faints when Marty approaches him. The film continues in Back to the Future: Part III

from wikipedia