Blue Ring Assassins - Blue Ring Assassins, #1

WWII historical fiction, laced with true events. Berlin 1939 - 1943 From the smoking ruins of a bombed Berlin brothel, three shocked and injured female survivors are taken to a secluded training facility by Nazi officer, Gruppenführer Walter Schellenberg. They're not there for official business but for medical treatment. Trained by the SS officer in all aspects of espionage, the women are desperate to survive.
They turn the tables on their armed captors and kill them. After covering their tracks, the women return to ply the only trade they know. with an added twist. Somehow these 'sisters in arms' escape the attention of the Nazis, despite the high rank of their victims, and their lucrative business thrives. They haven't escaped everyone's notice though. British Intelligence were monitoring Schellenberg's operations for some time, and their attention has zeroed in on the three women.
They dispatch one of their top male agents to make contact.