Film review: The Sessions, starring John Hawkes and Helen Hunt

During awards season one's instinct would be to distrust a true-life drama of the disabled, particularly one about a man crippled with polio who hires a professional to help him lose his virginity – "My Left Nut", as it were.

Resist your scepticism, because Ben Lewin's film is a miniature of comic sweetness and sorrow. Mark O'Brien, a Berkeley poet and essayist, had lived with polio since childhood, confined for most of the time to an iron lung. (He can last for three hours a day outside it.)

In his late thirties and lovelorn, he decides to act upon his yearning for physical intimacy by contacting a licensed sex surrogate, who will initiate him via "body awareness" sessions into the act of love itself.

What might have been corny or exploitative turns out instead to be tender and desperately moving. Its achievement lies partly in the casting. John Hawkes, known hitherto as the gimlet-eyed meth addict of Winter's Bone and the super-creep cult leader of Martha Marcy May Marlene, is a revelation as Mark, gracious and wry as he looks upward from his contorted horizontal trap (I kept turning my head to look at his face), his feathery voice modulating between uncertainty and hopefulness.

Matching the mood is Helen Hunt as Cheryl, the woman who will conduct Mark through the explicit physical challenges of sex and us through the potential awkwardness of watching them. Hunt's breeziness doesn't always endear, but here it's just right, warm yet matter-of-fact in dealing with her client, not least in the way she explains how she's not a prostitute. She also goes bravely naked, unlike him.

Writer-director Lewin doesn't finesse it visually much above made-for-TV standard, but he works wonders in the margins, notably with William H. Macy as a hip priest trying to help Mark square his devout Catholicism with his sexual needs. He superbly suggests a sympathetic listener who's receiving too much information. And as Mark's poker-faced yet capable assistant Moon Bloodgood is quietly charming. It could all have gone so wrong – but it never does.