Keane is not a nice film. It is tough, uncomfortable and hard to watch. Its realism is uncompromising, and it presents us with an ambiguous central character.

But it is a film that demands that the audience recognises its moral centre, and be forced into compassion for its protagonist.

William Keane, magnificently played by Damian Lewis, is a man on the cusp of madness. His six-year-old daughter has been abducted and Keane spends his days frantically (and often manically) searching for her in the Port Authority Bus Terminal in New York, mumbling paranoid mantras under his breath, ranting in the street, drinking heavily and sleeping rough.

Keane is in every shot of the film, and the camera is perpetually held in a head-and-shoulders shot of him. We are orientated either in front or behind him, there is very little in between, and we see only a smattering of life beyond the periphery of the frame. This is his world; grim, noisy, unlikable—and yet it's one we are forced to inhabit.

Despite Keane's apparent madness, we are shown that he can hold it together sufficiently to appear normal when interacting with others. It's this which allows him to form a tentative friendship with a single mother (Amy Ryan) in the same hotel as him, and her seven-year-old daughter, Kira (Abigail Breslin). We see how Keane would have once been a loving and responsible parent, and he is trusted to pick Kira up from school and take her out skating.

Keane's world sits on a knife edge between sanity and madness, and every scene is tainted with a gut-churning sense that he might blow it at any moment. He is conscious of his illness as much as he is consumed by it, and Damian Lewis captures this perfectly. In a lesser actor's hands the movie would fail, but Lewis imbues Keane with just the right amount of sympathetic characteristics for us to know that underneath his crushing madness he is a good person.

Director Lodge Kerrigan has visited the subject of mental illness before in Clean, Shaven which dealt with schizophrenia, but in Keane he has an arguably more complex protagonist.

Keane's world is washed out and grey, and set largely in busy public places—oilets, fast food restaurants, stations—but because we are glued to our central figure the effect is stifling. Kerrigan understands how to create a film which feels incredibly real, and not one of the performances is overstated.

Keane is a confrontational film that isn't pleasurable to watch. But it presents us with unusual subject matter in an idiosyncratic manner, and doesn't gloss over the often ugly nature of human beings. It will stay in your mind for days afterwards.