Helen Quilley (Creator/GwynethPaltrow) just got fired. And now she missed the [[UsefulNotes/TheLondonUnderground tube train]], too. Some kid was in her way, [[ForWantOfANail slowing her down for a second]].

But wait! [[AlternateTimeline She didn't miss the tube]]! The mother of the kid pulled the kid away, so Helen was never slowed down.

[[AlternateSelf The Helen who got on the tube]] meets an interesting guy on the tube, and when she gets home she catches her boyfriend cheating. She breaks up and gets an ImportantHaircut, turning blonde.

The Helen who missed the tube gets robbed, and comes home to be comforted by a boyfriend who had more time to cover his tracks a bit. She keeps her old hairstyle and remains brunette.

As time goes by, blonde Helen and brunette Helen live increasingly different lives. And yet they seem to somehow remember each other, each of them getting a sense of déjà vu when encountering something that is important in the counterpart's life.

!!This film provides examples of:

* AlternateSelf: Blonde Helen and brunette Helen.
* AlternateTimeline: Two time lines - one where Helen got to the tube and one where she didn't.
* AsYouKnow: Gerry's pal Russell spouts some exposition, to which Gerry repeatedly replies "I know!"
* BitchAlert: Lydia's EstablishingCharacterMoment is ''full'' of this.
* ExpositoryHairstyleChange: Without the difference in haircut, it would be hard to tell the two time lines apart.
* FlashSideways: Each Helen instinctively picks up on things important to the other Helen.
* {{Flatline}}: Used to show when one of the characters dies in one of the timelines.
* ForWantOfANail: A kid getting in her way for a second, making the difference between two radically different lives.
* ForeignRemake: The storyline recycles in a LighterAndFluffier way the plot of an earlier film, ''Film/BlindChance''.
* GirlishPigtails: Helen, when she has to work as a sandwich delivery girl and waitress.
* GreenEyedMonster: Lydia is this.
* HardDrinkingPartyGirl: Anna. Gerry nearly gets away with the extra wine glass in the laundry basket (left by Lydia) suggesting Anna left it there at one of their house parties. Anna admits it's something she'd probably do.
* ImportantHaircut: The change in hairstyle signifies a change in lifestyle.
* InSpiteOfANail: [[spoiler: Helen met James. Helen lost her unborn child. Gerry has impregnated Lydia. Helen has found out about Gerry and Lydia and has left Gerry. Which time line am I talking about?]] It's worth noting that all of those things come true in very different ways and at different times, however.
* IronicEcho: In the first time line when James and Helen meet he says "Cheer up, you know what the Creator/MontyPython boys say", and Helen replies "Always look on the bright side of life?" James then corrects her with "No one expects the Spanish Inquisition." When they meet again in the next time line he says the same thing and Helen responds with the latter line this time.
* KickTheDog: Lydia, who not only makes up a case of food poisoning just so she can harass Helen, but also [[spoiler:pretends she's interested in hiring her, just so Helen will show up at her apartment while Gerry is there so she can reveal Gerry's unfaithfulness to her in the cruelest way possible.]]
* LifeWillKillYou: [[spoiler:[[AlternateSelf One of the main characters]] is just standing there, having what would have perhaps been the most important conversation in a long and happy life. Suddenly a car runs over her. DownerEnding in one time line, but it is indicated that the trauma of her own death [[FlashSideways helps her]] to get a happy ending in the other time line.]]
* LoveTranscendsSpaceTime: Two time lines, two lives, one romance.
* UsefulNotes/TheLondonUnderground: The plot diverges at the main character catching / missing her train at Embankment station, setting off events for the rest of the film (which shows us two parallel lives from that point on). The actual scenes underground were filmed on the Waterloo and City Line.
* ManicPixieDreamGirl: Gender reversed. James is the Manic Pixie Dream Guy for Helen as he helps her to loosen up and enjoy her life, doing kind of silly things. And encourages her to [[StartMyOwn start her own business]] when she is fired.
* MirrorMonologue:
** {{Lampshaded}} after Gerry almost had his "secret romance" revealed to his live-in girlfriend:
-->'''Gerry''' [looking in the mirror]: You have two head problems. One, that was close, very close. Put in layman's terms, she nearly caught you. Two, and this is far more worrying than the first one, you're talking to yourself in the mirror again. Really bad sign.
** Later brought up again by his friend:
--->'''Russell''': You've been talking to yourself in the mirror again, haven't you?
* MissedTheBus: The plot is based on the difference it makes to this woman's life whether she gets or misses a tube train.
* PlotIncitingInfidelity: While the two timelines split with Helen missing the titular doors, the more important catalyst for divergence is when the Helen who caught the train walks in on her boyfriend cheating on her.
* ServiceSectorStereotypes: The worse-off scenario had the heroine fired from her job to become a waitress / delivery girl for a sandwich bar, much to the delight of her boyfriend's "other woman", who revels in exploiting and insulting her, knowing that her rival can't fight back.
* ShoutOut: Serious Beatles fans surely took notice when Helen and Anna direct the taxi driver to take them to "Number 9, Menlove Avenue". Menlove Avenue was the street in Liverpool where John Lennon lived for most of his childhood, and he had a thing for the number nine.
* UnusuallyUninterestingSight: Helen uses this for effect when she walks in on Gerry with Lydia. The first thing she remarks on is not [[YourCheatingHeart the fact he's in bed with another woman]], but instead [[SkewedPriorities the fact that she didn't think he liked]] Music/EltonJohn.
* WeAllLiveInAmerica: A small case but Helen and Anna reference ''Series/{{Jeopardy}}'', an American game show which does air on some channels in the UK but is unlikely to be talked about casually by two British women.