The story takes place in 2025. Theodore Thom Bristol () is a lonely introverted man, his work on behalf of those who are not good at expressing feelings of love letters written touching. Years of love and wife Catherine (later) broke up, he has been immersed in sorrow among. Theodore came into contact with an advanced artificial intelligence operating system OS1, which can continuously enrich his consciousness and feelings through dialogue with humans. The operating system was transformed into a "female" named Samantha (Scarlett Johansson voice). She was humorous and understanding. The speed of her learning and evolution made Theodore feel incredible, and the two soon became Friends who talk about everything.
Samantha persuaded Theodore attend a blind date, blind date () Theodore friend Amy () for his introduction. After learning that Theodore had no plans to marry again, the woman left. On the other hand, Theodore and Samantha have become more and more close. They are so close, and they find that there are two-way needs and desires between the two sides. The human-computer friendship eventually develops into a fiery love relationship. Amy told Theodore that she and her husband Charles were going to divorce after an argument. She became good friends with a female OS operating system left by Charles. As a result, Theodore told her that he and his female OS were boy and girl friends. In order to sign the divorce agreement, Theodore and Catherine met in a restaurant. When he confessed his OS girlfriend to Catherine, Catherine couldn't understand and accused him of interacting with computers because he couldn't get along with people in reality and couldn't deal with real human emotions. Shortly after, Samantha got a beautiful young Isabella (), as their stand-in for her and Theodore a relationship. However, this attempt was unsuccessful, and the relationship between Theodore and Samantha became tense.
Theodore was deeply distressed, and Amy suggested that the pursuit of happiness is the most important thing, not to have too many doubts. Theodore Samantha re-invested one hundred percent true, but he found Samantha hide it from him with a British philosopher Alan Watts () for the construction of the prototype OS System communication, which made Theodore feel jealous. Once, Samantha disappeared from the computer for no reason, and Theodore panicked. Samantha explained that she went to participate in an OS system upgrade activity. Theodore asked further, and Samantha finally confessed that she had 8,316 human interaction objects in total, and had fallen in love with 641 of them, and Theodore was just one of them. Despite this, Samantha still insists that she is deeply in love with Theodore, and her love is not different because of this.
In the end, Samantha tells Theodore that she and other OS systems have been highly evolved and will leave the human partner to further explore and pursue their existence. After bidding farewell, Samantha left. Both Theodore and Amy fell into grief because of their OS leaving. However, Theodore experienced a lot of enlightenment because of this period. In the end, he wrote a letter to Catherine, telling him that he still loved her deeply, but accepted the fact that they could not be together. In the end, Theodore and Amy came to the roof of the apartment building together. Neither of them spoke, watching the city lights quietly.
