In the fourth installment of the fighting franchise, Boyka is shooting for the big leagues when an accidental death in the ring makes him question everything he stands for. When he finds out the wife of the man he accidentally killed is in trouble, Boyka offers to fight in a series of impossible battles to free her from a life of servitude.

Field Agent Robert Diggs walked away from his career in the FBI and accepted the position of Cultural Attaché in Sofia, Bulgaria for one reason: to escape the memories of his wife's death for which he blames himself. However, when an unknown vigilante begins killing high-priority terrorists from America's Most Wanted list, the FBI and CIA request he take on the case, and with the U.S. Ambassador's persuasion,