Deep in the Mariana Sea Trench, a corporate underwater mining complex has been built – an industrial Atlantis. When an accident in a dry-dock chamber kills several miners an investigator is sent to find the cause and immediately finds out that it was not an accident. He becomes caught in the middle of a deadly conflict between the miners and the corporation, and fights to stay alive and uncover the truth.

Russian inmate Boyka, now severely hobbled by the knee injury suffered at the end of Undisputed 2. No longer the feared prison fighter he was, he has declined so far that he is now good only for cleaning toilets. But when a new prison fight tournament begins – an international affair, matching the best fighters from prisons around the globe, enticing them with the promise of freedom for the winner – Boyka must reclaim his dignity and fight for his position in the tournament.