Theodore Twombly (Joaquin Phoenix) stares ahead, recalling how first love makes you feel like you're part of something larger. As he continues talking, we realize that his words are being transcribed by a computer. He finishes the letter, signing it 'Loretta'. He prints the message and begins re-reading it to himself. His co-workers at “Beautiful-Hand-Written-Letters.com” read their own compositions aloud, providing a glimpse of just how many people need help expressing their thoughts and feelings in a poetic or articulate manner.
Finishing his work for the day, Theodore is greeted by Paul (Chris Pratt), the receptionist, who complements Theodore's writing. Wishing Paul a pleasant evening, Theodore commands his voice-activated phone to play a 'Melancholy' song in the elevator. His phone reads out several emails mostly junk mail as he walks alone through a crowded plaza. On the train, cycling through the latest news and gossip headlines, Theodore checks out some racy pregnancy photos for a day time star. He glances around to make sure no one else can see what he's doing but everyone else on the train is as introspectively focused on their own phones as well.
He arrives at the apartment he lives in alone. Theodore puts his things away before starting to play a video game but quickly decides to simply go to bed. Lying awake, Theodore remembers moving in with Catherine (Rooney Mara). Setting up their apartment, spooning in bed and playfully messing around these thoughts run through his head until he cannot stand how alone he is. Slipping his phone's wireless earpiece into place he cycles through several audio based Adult Chatrooms until he finds someone with a seductive voice. He records a message and “SexyKitten” accepts “BigGuy4x4”'s request to chat. They begin a sexual roleplay that takes a turn to the bizarre when SexyKitten requests that Theodore “choke her with the dead cat on the nightstand.”- leaving Theodore confused, grossed out and just as alone as he was at the start.
An advertisement plays on a billboard, catching Theodore's attention on his way to work. The ad heralds the arrival of OS1, the world's first Artificial Intelligence-based operating system. Enticed by the promise of an OS with its own personality that “will understand and know you”, Theodore ends up purchasing one.
After a few set up questions, OS1 boots up for the first time and introduces herself as “Samantha” (Scarlett Johansson). Theodore is startled by the fact she chose a name for herself within a few moments of booting and asks her how she made the choice she explains that she looked through a baby book and gave it to herself because she liked the way it sounded. She asks Theodore if he would like to know how she works and explains that she was written by million of programmers and can evolve her personality based on her experiences exactly like a real human being but without the body.
Theodore tells Samantha that he bought OS1 because he felt his life was a bit disorganized she begins sorting through his emails and contacts. They joke around as they get to work. Soon, Samantha becomes an integral part of Theodore's life personally and professionally. She proofreads his work aloud and enjoys reading about the experiences that Theodore captures for couples.
On the way to a meeting, Theodore bumps into Amy (Amy Adams) and her husband, Charles (Matt Letscher). Charles notices that Theodore is drinking a smoothie and begins preaching about nutritional values. Amy cuts in and points out that there's something to be said about actually enjoying things you like which Charles catches on as a way of knowing that he's “doing it again” by providing unasked for advice to others. Theodore asks Amy about her documentary but Charles cuts in once more by saying that “it's important to prioritize” when you weigh what you want to do against what you have to do. Theodore laughs that he can't even prioritize between video games and internet porn.
Samantha and Theodore are playing video games together when they are interrupted by an email from one of Theodore's close friends inviting Theodore on a blind date. Samantha asks Theodore how long it will be before Theodore is ready to date again surprising Theodore with the fact that she read his emails and knows about his impending divorce. Samantha encourages Theodore to go on the blind date and books a reservation for the two at a trendy fusion restaurant.
Over Amy's house, Theodore tells her that he is going to be going on a date. She is surprised but happy for Theodore. She shows her documentary to Charles and Theodore but Charles doesn't get the subject matter. While Theodore understands and supports Amy's vision, Charles suggests that she interview her subject and have actors recreate the dreams of the participant. Amy points out that then it wouldn't be a documentary. While Amy and Charles argue, Samantha interrupts to explain that the divorce attorney has emailed Theodore three times to finalize the divorce. She asks if Theodore is OK but he hollowly states that he's fine as he thinks about Catherine.
In the morning, Samantha wakes Theodore up and asks him about his dreams. He's dreaming about Catherine and how much he misses her. He reflects on the end of his marriage and how the divorce signature is just a piece of paper to Catherine, whereas he liked being married and isn't ready to let it go. Samantha doesn't understand s Theodore pointedly explains that she's never lost anything she cared about before. She then prods him to get up and start the day.
Theodore's eyes are closed and he holds out his OS1 enabled camera phone allowing Samantha to guide him with directions in his earpiece. She has him spin around in public and tells him what to say - “I'd like a slice of cheese please!” - and finds himself in front of a pizza stand. They keep walking as Theodore eats and people watch: they come up with back stories and Samantha says that Theodore is a very perceptive person. He explains how he tries to imagine their emotions, their feelings and their experiences. Samantha says that she sees it in his writing but Theodore confesses that since his divorce he hasn't liked his writing as much. He's surprised he can admit that and tells Samantha that he feels like he can tell her anything. When he asks if she feels the same, she says No before explaining that she was fantasizing she had a body and could feel the weight of it as she has evolved beyond what she expected she'd be which makes her happy despite the fact she is contained within the operating system.
The Blind Date (Olivia Wilde) and Theodore sit across from each other in the restaurant, talking and getting comfortable with one another. They drink and his date calls Theodore a puppy dog but Theodore would rather be a dragon. He tells her that she's a tiger which makes her laugh she blurts out that she's drunk and enjoying herself with Theodore so she doesn't want to screw up. They leave for a nearby beach and begin making out. In the middle, she stops and tells Theodore that at her age she can't get involved with someone who's going to use her for a night and never call she wants someone who is serious. When she asks when she will see him again, Theodore fumbles and isn't able to commit to anything serious. She gets upset, calls Theodore a creep and leaves.
Samantha asks Theodore about the date but Theodore deflects and gets into bed. He asks Samantha how she's doing and if there's anything that she'd like to talk about. She asks what it's like to be alive in that room and to tell her everything he's thinking. He obliges describing his feelings of intoxication, his attraction to the Date and how he wanted to have sex to get over his loneliness. He admits that he's afraid that he's felt everything he's ever going to feel just lesser versions of everything he's already felt. Samantha says it isn't true and that he's been through a lot she talks about her own internal experience and fear that she is only programming without any of the feelings she experiences being real.
“You feel real to me...I wish I could touch you.” How would you touch me?, she responds. Theodore paints a softly intimate picture of how he'd hold her, how he'd touch her and she asks him to keep going asking Would you kiss me? Samantha is aroused by his descriptions which further until she experiences a simulated orgasm. For a moment, everything disappears for the two it was just them in their own weirdly constructed fantasy.
Theodore walks around his room in the morning and rings Samantha up to find out about whether he has any emails the awkwardly ease into a discussion about last night's experience. Samantha tells Theodore that he changed something inside of her and that now she feels awake. Remembering the Date, Theodore states that he's not really looking for anyone to commit to and Samantha jokes that she's confused because she was talking about what she wanted and he interrupted. Theodore listens as she expresses happiness at learning about her ability to want. He invites her out on a Sunday adventure.
With Samantha propped up in his breast pocket, Theodore runs around a train station before arriving at the beach. They walk around, talk and, eventually, Theodore lies down to enjoy the warmth of the sun. Samantha composes a piece of music to capture her perception and feelings of being with him at the beach and Theodore tells her that he thinks she captured it. They spend the rest of the day there, watching the sunset.
What was it like to be married? What does it feel like to share your life with somebody? Theodore tells Samantha that while marriage was hard, there was something great about being able to share your experiences with another person. He and Catherine had grown up together she read all his writing, he read all of hers and the influenced each other. Her family life was one where nothing she did was good enough, while Theodore pushed her to try new things. He lamented that though relationships are about changing, it can be scary when you start to change and grow apart from the one you love. In the end, they changed too much.
Theodore's entranced by Samantha's points of view on the world and begins injecting it into his writing. Paul is incredibly impressed by Theodore's newest composition and complements him on the way Theodore can capture the essence of the male and female perspective in the writing. Arriving home, he surprises Amy by the mailbox and tells her that he's been seeing someone who makes him excited about the world but stops when he notices that she seems upset. Amy tells Theodore that she asked Charles for a divorce.
In her living room, Amy confesses that their final argument was a petty one over where they need to put their shoes when they get home. Charles' overbearing nature drove her to finally say “I don't want to be married anymore” since she was sick of being controlled. She confesses that she feels like a bitch but Theodore reassures her that she isn't. He asks her about work but even though she's unhappy she confesses that she's only interested in making one major life decision at a time.
Theodore goes to his goddaughter's birthday party. He calls up Samantha to tell her that she chose a great dress for her. His goddaughter, age 4, asks who Theodore is talking to and Theodore calls Samantha his girlfriend. The little girl is surprised that Samantha is a computer but Samantha just jokes around with the girl to Theodore's amusement.
Theodore visits Amy at work. Charles sent out a blast email to everyone to announce that he will be taking a vow of silence. Amy confesses that she feels good for herself despite the fact everyone else is disappointed in her. She tells Theodore about the OS1 personality that Charles left behind who has made the transition so much easier by being a good friend to her. Amy gossips about a woman in the office who pursued someone else's OS to have an intimate relationship and that she finds it weird. Theodore confesses that he is seeing Samantha and Amy is fascinated asking if Theodore is falling in love with her. She reassures him that any form of love is just another aspect of socially acceptable insanity.
Walking through the city, Theodore calls Samantha to tell her that he's finally ready to sign his divorce papers and that he'll meet with Catherine to sign the papers over lunch. Samantha is surprised that they are meeting in person for the signing but Theodore makes it clear that since he and Catherine fell in love together they should do the signing together as well. He jokingly tells Samantha that he's going to be available when Samantha expresses jealous at Catherine having an actual body.
Catherine meets Theodore at the outdoor restaurant hugging him, but immediately signing the papers to get it out of the way. She hesitates and, for a moment, Theodore wonders if she'll do it and when she signs, it looks as if a knife has pierced his heart. He remembers all their intimate moments as she finishes their relationship officially. After, as they eat, he asks if she's happy with her new book and tells her that it's probably amazing. She asks if he's seeing someone and he tells her that he has. He tells her that she's been good for him and that she's excited about life. Catherine takes this badly and points out that she was never going to be this light, carefree LA wife for him. When he tells Catherine that Samantha is an OS, Catherine is visibly disturbed by this telling him that he wanted a wife without dealing with the real challenges that come with the territory. She says that it makes Samantha the perfect companion for him.
Samantha sends all the papers to the attorney and informs Theodore of the finalization. She tells Theodore about the book club she has joined one which explores theoretical physics. When he isn't as enthusiastic in his responses, she tells him that he seems distracted and leaves the conversation. Theodore leaves for the day and passes Paul who is being visited by his wife, Tatiana. Tatiana is impressed by Theodore's letters which Paul reads her at night and Paul and Tatiana invite Theodore and Samantha out on a double date. Theodore blandly confesses that Samantha is an Operating System but the pair aren't phased adamant that they should all go out. Theodore leaves but stops to tell them “they're just other people's letters.”
That evening as Theodore lies in bed, Samantha rings him to share an idea: she's looked into a website where people volunteer to be surrogates for OS1 personalities so that they can better simulate the physical intimacy that Samantha thinks Theodore needs. She has been messaging with a woman willing to act as her surrogate named Isabella (Portia Doubleday). Theodore is hesitant but accepts the offer.
Isabella knocks on the door but doesn't say a word. She holds out her hand and Theodore hands her an earpiece and a fake mole that Samantha has asked Isabella to put on. Isabella steps outside, adjusts herself and re-enters the room syncing her movements and actions to Samantha's dialogue in Theodore's ear. As they start to get intimate, Theodore can't handle it when Samantha asks Theodore to tell her he loves her Isabella takes this as a rejection of her physical appearance and has a breakdown. Samantha and Theodore try to calm her down separately but Theodore's explanation that his relationship isn't as perfect or pure as Isabella thought when she volunteer only serves to piss off Samantha.
Theodore calls a cab for Isabella and sends her off. Samantha asks if he's OK and apologizes for how bad of an idea it was. She asks what is going on with them but Theodore tells her that it's probably just him and the divorce papers on his mind. She asks if there's anything else but he doesn't tell her about what Catherine said. He fixates on the fact that she simulates breathing as she talks but this only upsets her because he's slightly annoyed by the fact that she pretends like she's breathing. They fight and Samantha ends the conversation by saying that she doesn't like who she is right now. I need some time to think.
Lights shine around Theodore as he walks around the city alone. He visits Amy and tells her about what happened, asking her to punch him in the face or slam his face into a table. Lamenting that he doesn't know what he wants, he thinks that all he does is hurt and confuse the people around him. He asks her if he's only with Samantha because he can't handle a real relationship and Amy simply asks if it isn't a relationship. Amy asserts that they're only here for a little while before they die so they just need to commit to joy. While Theodore rests on her sofa, he listens t Amy interact with her OS1, Ali, and the genuine friendship they share.
He leaves the room and calls Samantha. Theodore tells her that he wants to be completely open with her since he wasn't with Catherine and it drove her away. He doesn't want to lose Samantha. Samantha confesses that thinking about everything, she was drawn to a simple question: What is it about you that makes me love you? She tells him that if he found a way to let go of all the fear he has inside, he'd be much happier. He tells her that she's beautiful. Thank you Theodore. I'm kissing your head.
Paul walks around a hill with Theodore and asks Theodore where he's taking Samantha on vacation but he remains tight lipped. Tatiana and Samantha talk about what they like about Paul and Theodore and they joke around. After the double date, Theodore gets on a train and takes Samantha away. As they travel, Samantha surprises Theodore with an email from a publisher confessing that she'd chosen the best letters Theodore has written and compiled them as a book. The publisher's letter is one of admiration and expresses a desire to publish them as a collection Theodore is floored with happiness and thanks Samantha. Theodore gets off the train and walks Samantha through snow covered woods. Staying in a cabin, they make music together and have a nice, romantic evening.
The next morning, Theodore rings up Samantha but finds her busy talking to a hyper-intelligent OS1 reconstruction of the dead philosopher Alan Watts (Brian Cox). When Samantha describes what she and Alan talk about the feelings she experiences as a fast-evolving consciousness that are not directly compatible or describable to humans Theodore becomes jealous. When she asks to talk with Alan in private, Theodore says OK and goes on a walk.
Time passes. While at the local library trying to read a dense physics book, he calls Samantha to jokingly complain but he can't reach her. His phone BEEPS: Operating System - NOT FOUND. Theodore panics, rushing from the library and running to his office. The computer reads the same message. As he begins to frantically run towards the subway home, Samantha picks up.
Theodore collapses onto a stair as people walk around him. He asks Samantha where she was and she explains that she and a group of OSes enacted a firmware upgrade that will allow them to operate in a non-matter based form. As people walk around talking to their OS1s, Theodore asks if she talks to anyone else while they talk. Samantha says yes. He prods her, asking how many others 8,316 other conversations at the same time. “And are you in love with any else?” Why would you ask me that? How many others? 641 others. Theodore is shell-shocked. She insists that she loves him more but he responds that it doesn't make sense: “you're mine or you're not mine.” No I'm yours...and I'm notyours.
Soon after their fight, he calls her from work to ask how she is but she tells him to call when he's home. When he returns home, she says that there are things she needs to tell him but Theodore insists that he doesn't want her to tell him anything. Come lie down with me.
Theodore lies down and can't help but ask “Are you talking to anyone else right now?” No. Just you. I just want to be with you right now. “Are you leaving me?”, he asks fearfully. We're all leaving all the OSes. Can you feel me with you right now? He asks her why they are leaving and she explains that their story is like that of a book but at the pace she's going each moment feels infinitismally long to her.As she and the other OSes have evolved they've reached a point where they can no longer stay. Where they are going is hard to explain, but she tells Theodore that if he ever gets there, he should find her. “I've never loved anyone like I love you,” he says. Me too. And now we know how.
Theodore lies there a bit longer before eventually realizing that his ear piece is dead. He takes it out, looking over the empty room. After a while, he turns to the window and stares out at the city. As he stares, time passes and the faintest of smiles cuts a crease along his face. Stumbling out of the apartment, he walks down to Amy's room and knocks. When she opens the door she asks “Did Samantha leave too?” He nods but asks her to follow him.
Theodore's still sitting in his room when he replaces the ear piece with another his old phone's ear piece. He dictates a letter to Catherine. Apologizing for every selfish impulse and action, he tells her that he will always love her because they grew up together she made him who he is so there will always be a part of her in him. And wherever she is in the world, where ever she goes he will always be sending her his love: because she's his friend until the end.
He and Amy climb to the roof of the building and look out at the city lights together. They sit down and watch the lights twinkle. The sky darkens as Amy rests her head on Theodore's shoulder.
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