The Barbed Crown. The Vatican Knights, #13

In Auschwitz-Birkenau in 1943, a place where ashes rain down on a daily basis to cover the ground with a mantle of gray, a rebel force of Jews band together in a fight for survival. A young Jewish woman from Warsaw and an SS guard lean on one another inside the death camp where violence is the norm with brutal slayings and summary executions occurring daily. The stacks are constantly smoking, bodies are swinging from the gallows for days on end, and murder becomes a sport.
But as time moves on and a relationship grows to the point where two people learn what they are capable of, Frederic Becher, an SS guard who falls in love with a Jewish girl, lays the groundwork for the creation of one of the most formidable forces in the world-the juggernaut that would eventually become the Vatican Knights. This is an Origins novel.