Cold-Blooded

Sam Abel is not in this adventure but it is part of the author's Whispers and Shadows spy series and in his words serves "as a bridge between books and introduced some new characters which will return".
"Roger Fowler’s time as a spy has come to an end. In Nazi Germany, the hunters are relentless, and even the best operators are at risk of being caught. When his enemies come knocking at his door, Roger has no choice but to surrender.
Now compromised, Roger is fearful of his ability to withstand torture and interrogation. The infamous spy hunter Aksel Falke, commonly known as Der Fänger , aims to test him. Word has traveled about Falke’s uniquely terrifying interrogation methods—and the results they yield."