Contemporary high schooler Marty McFly (Michael J. Fox) doesn't have the most pleasant of lives. Browbeaten by his principal at school, Marty must also endure the acrimonious relationship between his nerdy father (Crispin Glover) and his lovely mother (Lea Thompson), who in turn suffer the bullying of middle-aged jerk Biff (Thomas F. Wilson), Marty's dad's supervisor. The one balm in Marty's life is his friendship with eccentric scientist Doc (Christopher Lloyd), who at present is working on a time machine. Accidentally zapped back into the 1950s, Marty inadvertently interferes with the budding romance of his now-teenaged parents. Marty must now reunite his parents-to-be, lest he cease to exist in the 1980s. It won't be easy, especially with the loutish Biff, now also a teenager, complicating matters. Beyond its dazzling special effects, the best element of Back to the Future is the performance of Michael J. Fox, who finds himself in the quagmire of surviving the white-bread 1950s with a hip 1980s mindset. Back to the Future cemented the box-office bankability of both Fox and the film's director, Robert Zemeckis, who went on to helm two equally exhilarating sequels.

Plot
Marty McFly is a teenager living with a grim and bleak family in Hill Valley, California. His father, George, is constantly bullied by his supervisor Biff Tannen, and his slobbish overweight mother, Lorraine, has a drinking problem. On the morning of October 25, 1985, his friend and scientist Dr. Emmett "Doc" Brown calls him, asking to meet at 1:15 AM the following morning at Twin Pines Mall. Marty and his band audition to perform at the school dance, but are rejected. Marty's girlfriend, Jennifer Parker, encourages him to pursue the dream of being a rock musician. At dinner that night, Lorraine recounts how she and George first fell in love when her father hit him with his car.

Marty meets Doc as planned. Doc reveals a DeLorean DMC-12 which he has modified into a time machine, powered by plutonium which generates 1.21 gigawatts of power into a device he calls the "flux capacitor". Doc also explains that the car travels to a programmed date upon reaching 88 miles per hour. However before Doc can make a trip twenty-five years into the future, Libyan terrorists, from whom he stole the plutonium, show up and gun him down. Marty attempts to escape in the DeLorean but, in the process, reaches the speed of 88 miles per hour and is transported back to November 5, 1955.

In 1955, Marty runs into his teenage father George, who is being bullied by Biff. As George is about to be hit by Lorraine's father's car, Marty pushes him out of the way and takes the impact. As a result, Lorraine becomes infatuated with Marty instead of George. Marty is disturbed by her flirtations, and leaves to find Doc. Marty convinces Doc that he is from the future and asks him to help him return to 1985. Doc is aghast by the fact the time machine requires 1.21 gigawatts of power, telling Marty that the only possible source of that amount of power is a bolt of lightning. Marty remembers that lightning will strike the courthouse clocktower the following Saturday at 10:04 PM. Doc also deduces that Marty has prevented his parents from meeting. He tells Marty he must find a way to get them together or he will never exist.

Marty plans to have George appear to rescue Lorraine from Marty's overt sexual advances on the night of the school's "Enchantment Under the Sea" dance. However a drunk Biff unexpectedly shows up, pulls Marty from the car and forces himself on Lorraine. George arrives as planned to rescue Lorraine from Marty but finds Biff instead. Biff subjugates George, but George punches Biff in the face, knocking him out. A smitten Lorraine follows George to the dance floor, where they kiss for the first time, assuring Marty's existence.

Meanwhile, Marty writes Doc a letter to warn him of his murder in 1985, but Doc indignantly tears up the letter without reading it, for fear he will alter the future. The lightning strike at 10:04pm successfully sends Marty back to 1985. However, he is too late to prevent Doc from being shot, but Doc reveals he was wearing a bulletproof vest and confesses that he taped the letter back together.
Doc drops Marty off at home and leaves in the time machine for the future. Marty awakens the next morning to find his home and family significantly improved and happier. Lorraine is physically fit, George has become a self-confident and successful science fiction author, Marty's brother Dave is now a businessman, and Biff has become an auto-detailer, who is now deferring to George. Just as Marty reunites with Jennifer, Doc arrives, insisting that they accompany him to the future to sort out his children. They enter the updated time machine, now a hovercar, and blast into the future.