this is just my opinion and i may be wrong,
i believe that samantha is in control of the zombies, richtofen is on a mission for the illuminati trying to kill/destroy her and stop the zombie threat. but she is also trying to kill richtofen as he killed her and her father maxis. i believe that richtofen brainwashed , Tank, Nikolai, and Takeo. tank who was on amission to rescue peter (i think its peter-the guy hung on shi no numa) who was undercover for america, richtofen brainwashed them so that he has extra protection, as he knows he can not survive samantha alone. and the team now travel from base to base uncovering the experiments, and weapons created.
