Boyka (Scott Adkins) is a Russian inmate who used to be one of the fiercest and most successful fighters alive, constantly being the premier fighter in his prison. After suffering a knee injury sustained in his last fight, he no longer has the fighting ability or ferocity he once had. Everything changes, however, when he hears of a new fighting league. The league will bring together the best fighters from maximum security prisons all around the world, and the main point of the competition is as a means of gambling for the observers. But, the winner of the competition has something to gain, too - his freedom. Little do the fighters know, the winner will never see the light of day, and the organizers are just out for a quick buck.