Operation Darkness follows a squad of British SAS soldiers fighting the Nazis across the European Theater. The story covers much of the real history of the European war, including the battles for North Africa and the liberation of mainland Europe. French resistance fighters, American soldiers, and others appear as non-player characters. The game features Adolf Hitler as its final boss wearing a mecha-suit in clear reference to Castle Wolfenstein. The game diverges significantly from real history in that zombies of deceased Nazi soldiers appear as adversaries, and two of the player characters can transform into werewolves. Other fantasy elements include the appearance of supernatural foes such as vampires, as well as allowing the use of magic spells.