For the mission of Return to Castle Wolfenstein, see Dark Secret.

Episode Four of Wolfenstein 3D, titled A Dark Secret, is the first in the Nocturnal Missions trilogy of episodes which was initially sold separately from the game's first three episodes, later fully integrated into the game.


The Nocturnal Missions depict BJ Blazkowicz's struggle to end the German chemical warfare campaign (Giftkrieg - "poison war") . The first task, and the main goal of Episode 4, is to find and defeat the mad scientist behind the creation of the chemical weapons. After fighting through a weapons research facility, BJ approaches and defeats this scientist: Otto Giftmacher (Poisonmaker).