But wait! She didn't miss the tube! The mother of the kid pulled the kid away, so Helen was never slowed down.
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:
- Alternate Self: Blonde Helen and brunette Helen.
- Alternate Timeline: Two timelines - one where Helen got to the tube and one where she didn't.
- As You Know: Gerry's pal Russell spouts some exposition, to which Gerry repeatedly replies "I know!"
- Bitch Alert: Lydia's Establishing Character Moment is full of this.
- Bittersweet Ending: The timeline where Helen missed the train ends this way. Yes, she went through a longer time of being cheated on, had to work as a waitress after losing her job, and had a miscarriage after falling not long after she found out she was being cheated on, but she survived the accident unlike the other Helen, breaks up with Gerry and meets James when she leaves the hospital.
- Convenient Miscarriage: Helen gets pregnant in both timelines (Gerry in the one where she missed the train, and James in the one where she caught the train). She loses the baby in both timelines after an accident, before she gets the chance to tell them. However, this turns out to be for the best in the timeline where she missed the train, as she no longer has a reason to stay with Gerry, and eventually meets James when she leaves the hospital.
- Downer Ending: The timeline where Helen caught the train ends with her getting hit by a car, losing her and James' unborn child, and dying soon after while James cries over her.
- Expository Hairstyle Change: Without the difference in haircut, it would be hard to tell the two time lines apart.
- Flash Sideways: Each Helen instinctively picks up on things important to the other Helen.
- Flatline: Used to show when Helen dies in the timeline where she caught the train.
- For Want of a Nail: A kid getting in her way for a second, making the difference between two radically different lives.
- Foreign Remake: The storyline recycles in a Lighter and Fluffier way the plot of an earlier film, Blind Chance.
- Girlish Pigtails: Helen, when she has to work as a sandwich delivery girl and waitress.
- Green-Eyed Monster: Lydia is this.
- Hard-Drinking Party Girl: 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.
- Important Haircut: The change in hairstyle signifies a change in lifestyle.
- In Spite of a Nail: 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 are we talking about here? It's worth noting that all of those things come true in very different ways and at different times, however.
- Ironic Echo: In the first time line when James and Helen meet he says "Cheer up, you know what the Monty Python 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.
- Kick the Dog: Lydia, who not only makes up a case of food poisoning just so she can harass Helen, but also 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.
- Life Will Kill You: 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. Downer Ending in one time line, but it is indicated that the trauma of her own death helps her to get a happy ending in the other time line.
- Love Transcends Space Time: Two time lines, two lives, one romance.
- The London Underground: 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.
- Manic Pixie Dream Girl: 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 start her own business when she is fired.
- Maybe Magic, Maybe Mundane: Was there really something that caused the timeline to split, and to cause the Helen who missed the train to remember bits of the timeline where she caught the train? We may never know.
- Mirror Monologue:
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.
- Lampshaded after Gerry almost had his "secret romance" revealed to his live-in girlfriend:
- Later brought up again by his friend:Russell: You've been talking to yourself in the mirror again, haven't you?
- Missed the Bus: The plot is based on the difference it makes to this woman's life whether she gets or misses a tube train.
- Plot-Inciting Infidelity: 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.
- Service Sector Stereotypes: 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.
- Shout-Out: 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.
- Split Timelines Plot: The Trope Codifier - the two timelines split depending on whether Helen makes it to the Tube or not.
- Strangely Specific Horoscope: Played with in Sliding Doors. When Helen claims to be over her boyfriend Gerry, (who she recently dumped after she came home early from work and caught him cheating) Helen's best friend Anna calls her out for lying, noting that Helen is still counting the days since the breakup, and is still reading Gerry's horoscope in the hopes that it will say that something terrible will happen to him. Later Anna pretends that the horoscope does in fact say that something terrible will happen to Gerry in a way that would make the horoscope specific to Gerry.Anna: You're still counting how long you've been apart in days - and probably hours and minutes - but the big-flashing-red-light way of telling you're not really over someone is when you're still reading their horoscope in the hope that they're going to get wiped out in some freak napalming incident. [Later Anna looks at the horoscope] What is he?Helen: A wanker. [beat] Oh. Aries.Anna: Aries... Aries... well, just shows how much I know. [pretends to read] "With Mars your ruler in the ascendancy, you will get wiped out in a freak napalming incident and Helen says bollocks to you." This guy's very good.
- Unusually Uninteresting Sight: Helen uses this for effect when she walks in on Gerry with Lydia. The first thing she remarks on is not the fact he's in bed with another woman, but instead the fact that she didn't think he liked Elton John.
- We All Live in America: A small case but Helen and Anna reference 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.
- Your Cheating Heart: Gerry cheats on Helen with Lydia. In the timeline where Helen caught the train, she walks in on them and breaks up with Gerry. In the timeline where Helen missed the train, she doesn't walk in on them and stays with him for longer, but eventually Lydia leaves him, but soon returns to him to tell him she's pregnant and to discuss whether or not she will keep the baby. However, Helen finds out about this, leading to her falling and miscarrying her own baby. When she recovers, she breaks up with Gerry.