Set in Los Angeles in the slight future, Theodore (Joaquin Phoenix), a complex, soulful man who makes his living writing touching personal letters for other people. Heartbroken after the end of a long relationship, he becomes intrigued with a new, advanced operating system, which promises to be an intuitive and unique entity in its own right. Upon initiating it, he is delighted to meet "Samantha", a bright, female voice (Scarlett Johansson) who is insightful, sensitive and surprisingly funny. As her needs and desires grow, in tandem with his own, their friendship deepens into an eventual love for each other.