Joaquin Phoenix stars as Theodore Twombly, a former LA Weekly writer who now works for a firm called BeautifulHandwrittenLetters.com. As the film opens, he has been commissioned to write a love letter from a wife to her husband of 50 years. As he speaks to his computer, words appear on the screen. (However beautiful, the letters are not handwritten, nor even hand-typed, as keyboards have been banished from this particular future.) “Lying naked beside you in that apartment,” Theodore dictates, “it suddenly hit me that I was a part of this whole larger thing. Just like our parents, and our parents’ parents.”

Closed off and insecure in his personal life, Theodore pours his romantic self into these letters, loving vicariously as an intermediary for others. Recently divorced, tingling with loneliness, he grasps furtively for connection through phone sex and videogames. “Play a melancholy song,” he commands his ever-present handheld device—and when the chosen melody does not suit, “play a different melancholy song.”

Then he meets Samantha.

Or, to be more accurate, he purchases her. For Samantha—she chooses the name herself—is also known as OS1, the first artificially intelligent operating system. Theodore powers her up on his computer and at the first sound of her lively purr we can see that he is lost. Samantha is, after all, voiced (brilliantly) by Scarlett Johansson.

The love story that gradually unfolds is no less touching for its unorthodox structure. Samantha is in Theodore’s earpiece, in his handheld. He carries the latter around in his shirt pocket so that Samantha’s camera-eye can peek out at the wide world. Hers is the last voice he hears at night and the first he hears in the morning; she watches him as he sleeps. Over time, Samantha grows and learns, encountering selfhood, discovering her own wants, maturing at warp speed. Before long, Theodore is introducing her as his girlfriend.

Though intimate in scope, Her is vast in its ambition. Every time it seems that Jonze may have played out the film’s semi-comic premise, he unveils an unexpected wrinkle, some new terrain of the mind or heart to be explored. Though the relationship between Theodore and Samantha forms the movie’s central thread, Jonze weaves in a variety of intricate counter-narratives, alternative lenses through which to view his subjects of inquiry: Theodore’s own profession as a Cyrano-for-hire, a blind date gone awry, a videogame pantomiming parenthood, a visit from a sex surrogate that flips all the usual assumptions about what is real and what illusory. Meanwhile, Rooney Mara (as his ex-wife) and Amy Adams (as his closest friend) offer Theodore diametrically opposed—though individually persuasive—readings of his relationship with Samantha: a romantic dialectic.

As Theodore, Phoenix is heartbreaking in his vulnerability. Tender and tentative behind round glasses and a heavy moustache, Theodore is the super-ego that was somehow split off the raging id of Phoenix’s performance in last year’s The Master. Johansson is, if anything, a greater revelation still: Who imagined that, freed from the constraints of physical form, she was capable of such exquisite subtlety? Gentle, playful, easily wounded yet infectious in her enthusiasm, her Samantha is one of the more recognizably human characters of the movie year, binary code or no binary code.