Theodore is a professional writer who composes letters for people who are unable to write. Depressed and staying alone after his separation from his wife Catherine and the impending divorce, he buys an operating system integrated with artificial intelligence named Samantha that learns through experience. Theodore and Samantha get on well together in course of their regular conversation and the OS evolves day by day. After an unpleasant climax of a blind date, Theodore discusses his college date Amy with Samantha and mentions that they are good friends still. Theodore's relationship with Samantha brightens his days and their intimacy over verbal conversation grow, and this makes Theodore sign the pending divorce papers. Things get even more surreal when Samantha convinces a reluctant Theodore to use a surrogate date to add physical intimacy to their virtual relationship. Theodore finally agrees to bring in a surrogate date Isabella but ends up hurting her feelings. Samantha, without Theodore's knowledge, compiles his writings and sends them for publication which surprises him. Tragic elements are added to the story when Theodore learns that Samantha is simultaneously talking to hundreds of people and his relationship with her is not exclusive.