The player will have to be in the shoes of Agent 2 from the Office of Secret Actions (OSA), named William "BJ" Blazkowicz, who was the main character of Wolfenstein 3D. He was captured on March 17, 1943, and sent with Agent 1 to the prison at Castle Wolfenstein, where Agent 1 dies under torture.
The main plot will develop in Chapter 3 (Return to the Castle)