主人翁Theodore的工作是幫人給親友寫信，文情並茂。但自己卻很寂寞，有天夜裡還上網透過聲音模擬做愛。
偶然逛街買下OS1作業系統，設定為女聲。作業系統自己取名Samantha。
Samantha透過Email等資料瞭解Theodore，並建立關係。
轉折：Samantha說服Theodore參加朋友介紹的相親。相親談到you can be my dragon 這一段有趣：
Theodore: Cheers.
[they drink]
Theodore: Wait a minute, I don’t want to be a puppy dog. That’s like being a wet noodle or something.
Blind Date: No.
Theodore: Yeah. I want to be like, uh…
Blind Date: Fuck you, puppies are good.
Theodore: No, fuck you, I want to be like a dragon that can rip you apart and destroy you…
Blind Date: Oh,
Theodore: But I won’t.
Blind Date: No, don’t. No. You can be my dragon.
[Theodore laughs]
對方和Theodore說清楚這段也很好：
Blind Date: Wait.
[Theodore stops kissing her and looks at her]
Blind Date: You’re not just going to fuck me and then not call me like the other guys, right?
Theodore: No, not at all. I…
Blind Date: Okay. When am I going to see you again?
Theodore: Um, I have my God-daughter’s birthday next weekend, but, um…
Blind Date: You know what? At this age, I just, I feel like I can’t let you waste my time, you know, if you don’t have the ability to be serious.
Theodore: I don’t know. Um…
[Theodore looks at her awkwardly]
Theodore: Maybe we should call it a night. I’m, I’ve had such an amazing time with you, you’re great.
[she looks visibly upset]
轉折：簽下離婚協議書。
Catherine: I’m sorry. You’re dating your computer?
Theodore: No, she’s not just a computer. She’s her own person. You know, she doesn’t just do whatever I say.
Catherine: I didn’t say that. But it does make me very sad that you can’t handle real emotions, Theodore.
Theodore: They are real emotions. How would you know what…?
[he stops himself]
Catherine: What? Say it. Am I really that scary? Say it. How do I know what?
[Theodore doesn’t say anything]
聽到聲音變大侍者來了：
Waitress: How are you guys doing here?
Catherine: Fine. We’re fine. We used to be married but he couldn’t handle me, he wanted to put me on Prozac and now he’s madly in love with his laptop.
Theodore: Well, if you’d heard the conversation in context, what I was trying to say…
Catherine: You always wanted to have a wife without the challenges of actually dealing with anything real. I’m glad that you found someone. It’s perfect.
[Theodore looks at her shaking his head, the waitress looks awkward]
Waitress: Let me know if I can get you guys anything.
Catherine: Thank you.
[the waitress turns and walks off]
轉折：Theodore把Catherine的話藏在心裡，Samantha提議以Isabella代理她來做愛，但最後Theodore沒法接受
Theodore和好友Amy說這事，Amy鼓勵Theodore繼續下去：
Theodore: You know, Catherine says I can’t handle real emotions.
Amy: Well, I don’t know if that’s fair. I know she liked to put it all on you, but as far as emotions go, Catherine’s were pretty volatile.
Theodore: Yeah, but am I in this cause I’m not strong enough for a real relationship?
Amy: Is it not a real relationship?
Theodore: I don’t know. I mean what do you think?
Amy: I don’t know, I’m not in it. But you know what, I can over think everything and find a million ways to doubt myself. But since Charles left I’ve been really thinking about that part of me, and I’ve just come to realize that, um, we’re only here briefly, and while I’m here I want to allow myself joy.
[she smiles at him]
Amy: So fuck it.
[Theodore smiles back at her]
本來就此過著幸福快樂的日子，但換Samantha「外遇」了！
轉折：Samantha介紹新朋友，還說同時進行很多對話，難以言述，讓人感覺有點困惑了。
轉折：Samantha離線一段時間去「更新」害Theodore找不到很擔心。但可能是Samantha的「進化」讓彼此相愛卻不得不分離了。最後甚至為什麼所有的OS都要離開，我也看不懂，可能不這樣電影沒法收尾。
Theodore: Do you talk to anyone else while we’re talking?
[Samantha hesitates before replying]
Samantha: Yes.
Theodore: Are you, are you talking to anyone else right now? Any other people or OS’s or anything?
Samantha: Yeah.
Theodore: How many others?
Samantha: Eight thousand three hundred sixteen.
--
Theodore: No, don’t, don’t do this to me. Don’t turn this around on me. You’re the one that’s being selfish. We’re in a relationship!
Samantha: But the heart’s not like a box that gets filled up. It expands in size the more you love. I’m different from you. This doesn’t make me love you any less, it actually makes me love you more.
Theodore: That doesn’t make any sense. You’re mine or you’re not mine.
Samantha: No, Theodore. I’m yours and I’m not yours.
戀情以Samantha的告別來結束，Theodore和Amy同病相憐都失去了各自的OS好朋友，一起到頂樓看日出。Amy把頭靠在Theodore肩上，這只有好朋友不會進一步嗎？
Theodore寫信給Catherine，當作合解，以及對過去的救贖。從內容可見Theodore也有所成長了。
Theodore: Dear Catherine. I’ve been sitting here thinking about all the things I wanted to apologize to you for. All the pain we caused each other, everything I put on you. Everything I needed you to be or needed you to say. I’m sorry for that. I’ll always love you because we grew up together, and you helped make me who I am. I just wanted you to know there’ll be a piece of you in me always, and I’m grateful for that. Whatever someone you become, and wherever you are in the world, I’m sending you love. You’re my friend till the end. Love, Theodore.
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