Modern love - what is that these days? What constitutes a real romance? If the majority of our waking hours are spent online then what is real and what is not? Spike Jonze, returning after the rather unfair hammering of Where The Wild Things Are, asks this, and explores his favourite theme of alienation in this touching sci-fi drama.

Lonely and depressed over his impending divorce to Rooney Mara, Phoenix employs the help an OS, an intelligent interactive operating system that helps organise his life. Installed on his computer and phone, the OS becomes sentient, it gets to know him, adapts a personality to suit his, and becomes his confidant. Phoenix and his OS, Samantha (Johansson), blur the lines of what is a real romance and what is simulation…

Emotional detachment dominates the film, with an air of loneliness and desperation blanketing every scene. Phoenix is a professional romantic letter writer, which, in the very near future where the story is set, is a lucrative job that allows him to be romantic and sensitive for those who can't (or won't) be. He has no connection to the words he writes.

Although it has elements of humour, Her is essentially an existential melancholic tale of disconnection. The more we learn about Phoenix the more we learn why he falls for this disembodied voice: Samantha is always there for him, to help him, to laugh at his jokes. It's all one way. He doesn't have reciprocate. As Phoenix's work colleague exclaims, "I wish someone would love me like that."

It might cover the expected questions - like what happens when an artificial intelligence questions its existence - but Her isn't content to glide along on clever sci-fi ideas. As with the other recent real/unreal romance, Lars And The Real Girl, it continually surprises and concentrates on the emotional impact on the characters. And Jonze litters it with little Jonze touches, like the safety pin in Phoenix's front pocket that helps ‘Samantha' peek out and share what Phoenix sees as he goes about his day. Any other director would just ensure that Phoenix's front pocket would be small enough to snugly fit his phone.

It's a small thing but it's indicative of the care and effort Jonze goes to here.