Crime and punishment are viewed from a fresh perspective in The Work, a wide-ranging documentary that won the Grand Jury Award at this year's SXSW. An acutely observed account of a group therapy session within the walls of Folsom State Prison, it challenges the purpose of incarceration without end and the restrictive expectations of modern masculinity. The result is an emotional journey that resonates well beyond this hidden corner of America.

Folsom is a maximum security prison in California populated by men convicted of the most violent crimes, mostly related to drugs offences and gang rivalries. Many of them know they will never see the outside world again. Twice a year, members of the public are allowed to join prisoners for four days of intense therapy.

The Work selects three of the incomers from one session: bartender Charles, museum associate Chris and teacher's assistant Brian. All of them have issues they want to explore and all of them arrive with varying degrees of scepticism about the therapy. What follows is a raw account of their experience in which director Jairus McLeary and co-director Gethin Aldous appear to have won a huge degree of trust. The film is unfiltered and uncompromising, with camerawork that places the viewer right in the middle of the action. We hear tales of absent fathers, low self-esteem and the sense of lives that don't matter and will never amount to anything. 'I want to stop being my own worst enemy,' vows one prisoner.

Souls are bared, vulnerabilities are confronted – there are explosions of violence, primal screams of anger and bitter tears of release. Anyone dubious about the process is faced with the proof of their own eyes in a film that never feels voyeuristic or exploitative and remains gripping throughout.

Limited release from Fri 8 Sep.