Benn, James R. Billy Boyle World War II mystery

"Just days after the Liberation of Paris, Billy and Kaz are brought to Saint Albans Convalescent Hospital in the English countryside. Kaz has been diagnosed with a heart condition, and Billy is dealing with emotional exhaustion and his recent methamphetamine abuse. Meanwhile, Billy's love, Diana Seaton, has been taken to Ravensbruck, the Nazi concentration camp for women, and Kaz's sister, Angelika, who he recently learned was alive and working with the Polish Underground, has also been captured and transported to Ravensbruck. This news is brought by (retired) British Major Cosgrove, whose asks Billy for help, unofficially, in solving what he thinks was the murder of a British agent recuperating at Saint Albans. The convalescent hospital is really a secret installation for those in the world of clandestine warfare to recover from wounds, physical and emotional. Some are allowed to leave; others are deemed security risks and are kept in virtual imprisonment. When a second body is found, it is evident that a killer has found his or her way into this high-security enclave"--