Living in Bangkok, where he fights bare-knuckle in the local gyms, heroin addict Billy Moore (Joe Cole) is arrested and sent to Klong Prem jail for selling drugs. There, unable to speak the language, it's a matter of daily survival, as he is forced to live in unimaginable, unsanitary conditions, forever fearful of beatings from guards and other prisoners. It's only when Billy takes up Muay Thai boxing that he is able to see a way out of this hellish environment.