Timeline 2 or Timeline A is the timeline brought into existence by Marty's unintended alteration of history during his week in 1955. When Marty returns to 1985, ten minutes before he left, he watches himself from a distance. However, Marty's own memories are different than those of the Marty whom he sees jump into the DeLorean and travel into the past.
When Marty returns to 1985 from 1955, the first hint that his present has been altered is the broken ledge on the Courthouse. The ledge was unbroken when Marty was talking to Jennifer the previous afternoon. Now it's been broken for almost 30 years, exactly in the place where Doc Brown had stepped on it in 1955. A more obvious sign that the world has changed is that what was once called Twin Pines Mall is now the Lone Pine Mall. Marty witnesses his alter-ego escape into a past that has already been rewritten, giving way to Timeline 2.
In this timeline, Doc had worn a bullet-proof vest underneath his radiation suit. Here, Doc has been waiting for almost 30 years to watch the events of October 26, 1985, unfold, and has had the benefit of Marty's letter to warn him that he would be shot by terrorists (Doc has had to operate on the assumption that a vest would be enough, and perhaps has guessed that Marty's warning would otherwise have been more explicit).
When Marty awakes the next day, his bedroom is exactly as it was in Timeline 1. When he walks into the kitchen, however, he finds that the furnishings are more expensive, and that his brother and sister have changed. Dave, who had been working at a Burger King, now works at an office at an indeterminate job. Linda, who had been lonely, now wears contacts and is popular. Marty's Mom and Dad "look great". His father has published a novel, A Match Made in Space, which is apparently based upon Marty's "Darth Vader from the planet Vulcan" scheme in 1955. George's wrecked car has been replaced by a BMW, and George employs Biff's Auto Detailing to keep the McFly vehicles washed and waxed. Biff, who had been George's tyrannical boss, now addresses George as "Mr. McFly". Finally, Marty now owns the Toyota 4 x 4 truck that he had dreamed of in Timeline 1.
As Doc Brown points out in Back to the Future Part II, when leaving Jennifer behind in the alternate 1985, there is only one reality (rather than a series of parallel universes. The family photograph and the 2015 newspaper confirm that when the past is altered, items from the previous timeline change accordingly. This phenomenon is seen again with the alteration of other newspapers and photographs. As described in the Starlog magazine article, "The Other Marty McFly", the person seen escaping into the past at the end of the film has grown up in a different reality than our Marty McFly. Because of changes wrought by Marty's presence in 1955, the 1985 of Timeline 2 is, of necessity, different:
- It is more likely that Marty would drive his 4 x 4 to Doc's home, and then on to school, although he would still be tardy.
- Mr. Strickland can no longer claim that "No McFly has ever amounted to anything in the history of Hill Valley", in that George has been successful; however, Marty would still be a slacker, who needs to be "more like his old man".
- Though Marty might still be rejected at the audition, Jennifer would remind him that one rejection isn't the end of the world, and point to the good advice that "If you put your mind to it, you can do anything." In Timeline 2, however, that advice has come from Marty's father, rather than Doc Brown. In fearing rejection, Marty is no longer starting to sound like his old man; if anything, he would be worried that he will not be as successful as his father has been.
- In Timeline 2, Marty already owns a truck identical to the 4 x 4 that he sees at the Texaco station. It is likely that when he talks about "someday", he will be dreaming of an even better vehicle. Another possibility would be Marty musing about how he has a truck just like it, and anticipating the night at the lake.
- In Timeline 2, Marty's Mom does know about tomorrow night, and has no objections to Marty and Jennifer going up to the lake. It's likely that she has still given him "the standard lecture" about things she didn't do when she was his age, and Marty probably still thinks that "the woman was born a nun". On the other hand, she would maybe be much more understanding of how teenagers could be.
- The conversation might be different, but Marty is destined to be at Courthouse Square, where the "Clock Tower lady" will hand him the flyer (presumably, the Preservation Society also wants the broken ledge preserved exactly as it was).
- As established at the end of BTTF, the family car is not wrecked. Marty might be pouting over something else when Jennifer calls twice, but it isn't about a lack of wheels.
- If there is a confrontation between George and Biff in 1985, it isn't over George having to do Biff's reports, because George and Biff move in different circles.
- George and Dave would no longer be trying to advise Marty to avoid "headaches", nor discourage him from trying to work with his band.
- According to the deleted scenes of Part II, it was likely that Joey Baines was also imprisoned in this timeline. Thus, Lorraine would likely still be discouraged about Uncle Joey not making parole - and suggest that the kids "send him a line". Marty would likely still respond with the "Uncle Jailbird Joey" comment, and Dave and Linda would likely still express embarrassment in him.
- But most notably, Grandpa did not hit Dad with a car in this timeline, and Lorraine has a different story about she and George met; one in which he was heroic rather than helpless, and rescued her from Biff, "fighting for the woman he loved". What happens in 1955 after Marty from Timeline 2 escapes into the past would be similar, but Marty's perspective of what was supposed to happen would be different.
- Saturday, November 5th:
- Marty McFly arrives in 1955 from Timeline 1, on Old Man Peabody's farm, and knocks down one of Old Man Peabody's twin pine trees, fulfilling destiny.
- Marty runs into George at Lou's Cafe, and is surprised to see that George has not yet learned to stand up to Biff.
- Marty inadvertently becomes Lorraine's crush when he pushes George out of the way of Sam Baines's car and gets struck. The story of his parents' meeting that Marty has heard was that George had come to Lorraine's rescue. Given Sam's comment that "Another one of these damn kids" jumped in front of Sam's car, it's possible that Marty has heard that his grandfather had hit someone once before. From Marty's point of view, he has somehow unravelled the possibility that George and Lorraine will meet.
- As before, Marty finds the young Doc Brown and reveals that lightning will strike the clock tower next Saturday. And, as before, the picture of the McFly kids is altering because Marty has somehow interfered with the meeting of his parents. Although Marty isn't sure how George will go to the dance at all, let alone become Lorraine's rescuer, he knows that he has to make that event happen.
- Marty spends the next few days trying to get George to ask Lorraine to the dance, although George wants to stay home to watch Science Fiction Theatre. Marty is aware that George writes science fiction stories (in Timeline 1, he never knew that his Dad did anything creative), and decides to act out the story from McFly's novel, A Match Made in Space. Thus, he still plays the role of "Darth Vader from the planet Vulcan".
- The next day, however, Marty makes things worse when he punches Biff and eludes his pursuers on his skateboard at Courthouse Square, becoming Lorraine's "hero". As before, Marty has caused Biff to wreck his car. Marty must find a way for George to fight Biff, and for George to become the hero instead. As before, Marty concocts a plan for George to rescue Lorraine from Marty (from Marty's point of view, it would be better if George rescued Lorraine from Biff, but it seems unlikely that this would happen). Marty repeats to his father the advice that his father has always given to him-- if you put your mind to it, you can accomplish anything.
- Biff, who is paying the bill on his tidied-up car, boasts to Lorraine that he will marry her someday. She has just picked up her outfit for the dance at the frock shop, and rebuffs his advances: “I wouldn’t marry you if you had a million dollars”. Biff jumps into his car to go home to get ready for the evening. There is nobody with him.
- Marty observes that Dave, and then Linda, have disappeared from his photograph from the future, indicating that the current timeline has already changed into a timeline in which they will never be born. He looks noticeably concerned.
- Marty borrows Doc’s car to take Lorraine to the dance, but is having difficulty with going through with his side of the scheme. It appears that George won't be "rescuing" Lorraine from Marty's "advances", but Biff shows up instead. As before, George comes to Lorraine's rescue, and punches Biff, fulfilling the story that Marty of Timeline 2 has always heard. At the same time, Marty has inadvertently caused Marvin Berry's injury, and has to play at the dance in order for George and Lorraine to kiss. As the photo confirms, Marty himself begins to be “erased from existence.”
- While George and Lorraine are finally beginning to enjoy themselves at the dance, Dixon cuts in. George nevertheless takes what is rightly his and the future Mr. & Mrs. McFly finally share their first kiss. A timeline in which George's and Lorraine's three children were never born has again been averted, as Marty observes from his photo. Marty offers additional advice to his young parents in order to assure that he will have a nice life back in '85.
- At 10:04 p.m., lightning strikes the clocktower, and Marty travels back to 1985 in the time machine, via a complex utilization of the energy of the lightning strike itself devised by Doc Brown, and thanks to Marty McFly’s precise foreknowledge of this local historic event. There are no reported immediate witnesses to this event. Perhaps because of budget problems, or a lack of insurance, the clock is never successfully repaired; in fact, some Hill Valley residents voice a desire for the clock’s preservation as is (along with the damaged ledge below it) to memorialize the unusual occurrence.
- 10:05 p.m.. The young Doc Brown returns home, unnoticed, having witnessed the earliest successful demonstration of time travel in human history. As before, Doc is carrying a note Marty has handed him in lieu of verbal information about his own future, but is hesitant about reading it. In Timeline 2, Doc now lives with the knowledge that he will be successful in building a time machine, that Marty will be born in about thirteen years, and that seventeen years after that, Marty will have to be the person who travels back in time, or a paradox will occur.
- Saturday, November 5th:
When Marty of Timeline 2 returns home, he will not notice that anything is different in his own life, and conclude that things turned out as they were supposed to.
- Date unknown George and Lorraine get engaged, then married. Doc has avoided running into either of them, although Lorraine had followed Marty to Doc's workshop in 1955. Although Doc might read about the engagement and marriage, along with other McFly family news, in the Hill Valley Telegraph, he makes it a point to stay far away from the McFly family over the next several years so as not to endanger Marty's existence.
- 1962 Doc's mansion is destroyed by a fire. Marty knew that part of history, but had enough trouble in persuading Doc to be careful in 1985, let alone 1962.
- 1968 Marty McFly is born. Doc has been waiting to see whether this specific event would occur as predicted. Although he no longer has to worry about endangering Marty's existence, Doc knows that he will have to meet Marty at some point prior to 1985.
- Thursday, March 15th: George McFly wins an award for his writing, and the news is on the front page of the Hill Valley Telegraph the next day. At this point, Marty would be four years old. Doc reads about George's award, and figures on meeting Marty in another ten years. In this timeline, perhaps after hearing the story about how George stood up to Biff, Marty grows up with an insecurity that people will think that he's "chicken" (the Marty of Timeline 1 had proven his fearlessness a number of times). At some point, Marty will meet Douglas Needles, who may or may not have existed in the first timeline. Needles enjoys watching Marty's reaction to being called "chicken".
- 1981 Doc recognizes pictures of the brand new DMC-12 automobile, produced by the DeLorean Motor Company. Although he hasn't seen a DeLorean for more than 25 years, he makes plans to acquire one of the stainless steel vehicles at some point prior to 1985. However, Doc also knows from the videotape that Marty won't actually see the time vehicle until October 26.
- Date unknown Marty strikes up a friendship with Doc. Doc knows, from having set the controls on the time machine, that the time machine will have to be completed by October 26, 1985.
- January 1: At some point, Doc has used tape to put Marty's 1955 letter back together. Since Marty had written "Do not open until 1985", Doc has probably waited until 1985 to read the letter.
- Date unknown: Somewhere other than Hill Valley, Doc meets with some terrorists from Libya and agrees to build an atomic bomb for them if they can obtain plutonium. By October, the plutonium has been acquired and Doc delivers them a bogus weapon. Doc knows, from Marty's letter, that the terrorists will shoot him on October 26, and that he must take precautions. Since Marty didn't describe anything graphic, Doc hopes that a bulletproof vest will be sufficient. Doc continues to work on the time vehicle, and conducts an experiment that is intended to render all the clocks in his laboratory to be exactly 25 minutes slow.
- Friday October 25 Doc calls Marty at the laboratory sometime before 8:25, in hopes of learning whether his clock experiment worked. Doc asks Marty to meet him at the Lone Pine Mall at 1:00 in the morning, with the foreknowledge that the time displacement must take place at 1:34 am.
- Saturday, October 26:
- At 1:24 a.m., Marty and Doc are in the parking lot at the Lone Pine Mall (three minutes after Einstein's first trip through time). Meanwhile, across town at 1:24 a.m., an older Marty arrives from 1955 (Doc, however, assumes that Marty would arrive downtown at 1:34, the time that Doc set the controls for in 1955).
The rematerializing DeLorean fails to stop and crashes into the front of the Town Theatre (now used for a Christian revival congregation). He then runs from the town square over to the Lone Pine Mall to witness the departure of his one-week-younger self, and finds out Doc survived because he was forewarned by the note Marty gave Doc just moments ago in 1955 about the Libyans (and that Doc finally had the courage to read in his long interim). Doc retrieves the time machine before any witnesses arrive to the rundown square, and no charges are lodged against driver or scientist.
- Doc takes Marty back to his home, and then travels to 2015.
- (Saturday morning) Marty awakes at 10:28 a.m., thinking that he may have had a very detailed nightmare, but finds that things are as they should be in Timeline 2. As he walks out to the kitchen, he finds Dave and Linda eating breakfast, and watches as his parents walk in from having played tennis. When he hears his father talking to Biff, a look outside confirms that Biff is waxing the BMW. George confronts Biff over Biff's claim that he was just finishing up the second coat of was, and his parents remark that if it hadn't been for Biff, they never would have gotten together. Marty is relieved that he didn't mess up history, and concludes that over the course of 30 years, his parents forgot about the stranger who also helped them meet. When Biff brings Marty the keys to the 4 by 4, there's no surprise. Marty inspects Biff's work (knowing from experience that Biff cuts corners), and is looking forward to getting in the truck and going over to see Jennifer, whom he hasn't seen in over a week. However, she has arrived at his house.
At this point, the timeline would be altered by Doc's arrival from 2015. However, in Timeline 2, if Doc doesn't arrive, Marty and Jennifer would have a fun weekend, and plan a trip to the lake. This would set up the events of...
- Sunday, October 27th: Marty, accused by Douglas Needles of being "chicken", races Needles and crashes into a Rolls-Royce. He breaks his hand, and gives up playing guitar. The owner of the Rolls-Royce presses charges. Marty's life over the next several years is one of disillusionment and misery. Marty wonders if he'll ever see Doc Brown again.
- Date unknown: Roberta Needles, older daughter of Douglas, is born.
- Date unknown: Amy Needles, younger daughter of Douglas, is born.
- Date unknown: Grays Sports Almanac is published.
- 2000s - 2010s
- Date unknown: The Hill Valley Telegraph closes or sells its printing and news-gathering operations to USA Today to create a local edition of the nationwide newspaper.
- Date unknown: Invention of: hover conversion, Mr. Fusion, the Black & Decker hydrator, hoverboards, power shoelaces and self-drying jackets, skyways, rejuvenation clinics, suspended-animation kennels, automated gas stations, automated dog-walking leashes, thumbprint ID verifications, the 300-plus channel universe, automated hovering news units (as used by USA Today), roll-down television sets (the McFly home runs the Scenery Channel on it in a window).
- Date unknown: The United States abolishes the trade of lawyers, allowing the justice system to move with far greater speed and efficiency.
- Date unknown: The Weather Service develops the ability to control the weather.
- Date unknown: Relations with Vietnam improve and now there are promotions to surf there.
- Date unknown: Pepsi introduces Pepsi Perfect, a vitamin enriched cola (Marty orders this from the video waiter at the Café 80's).
- Date unknown: Pizza Hut introduces the dehydrated pizza that Lorraine McFly cooks in the hydrator.
- Date unknown: A woman becomes President of the United States (she is mentioned in the 2015 newspaper).
- Date unknown: Jaws 19 debuts at the theater: this time, it's really really personal.
- Wednesday, October 21st:
- Marty Jr. is pushed by Griff to participate in a crime. Asked whether he's in or out, Marty says he's "in".
- The 47-year-old Marty, dared by Needles, illegally lets Needles scan his card, and subsequently is fired by Ito Fujitsu in typical real-estate mogul fashion: “Read my fax!”
- Marty Jr. doesn't talk to Marty about what Griff is pressuring him to do.
- Thursday, October 22nd: Marty Jr. is tried, convicted and sentenced to 15 years in jail for a robbery.
- Monday October 26th: Doc Brown arrives in 2015 thirty years after departing October 26, 1985.
- Wednesday, October 28th: Marlene McFly attempts to break her brother out of prison. She is sentenced to 20 years in jail.
- Dates unknown: Doc spends an unknown amount of time in 2015 and later. While he's there, he outfits the time machine with a Mr. Fusion and a hover conversion, undergoes personal rejuvenation surgery. It's not known whether Doc sought out Marty (as he had promised in 1985), but Doc has learned about the disaster that tore the McFly family apart, and tracks it back to Marty Jr.'s meeting with Griff on the 21st. Eventually, Doc leaves for 1985 to fetch Marty and Jennifer. This creates Timeline 3 which begins at the Doc's entry point of 1985 and timeline 2 fades away.