The Third Circle — Brendan Howley

When Nikolai Chertkov returned home to the Soviet Union from German prison camp he juggled the roles of GRU translator and U.S. mole until the late 1960s. Warned just in time that he's about to be discovered, he flees Moscow in a trainload of Jewish refugees bound for Vienna. He is met by Marty Prevadello, a U.S. agent forced out of retirement solely to bring him in. Multiple interests monitor the improbable pair from Austria to an Alpine monastery, where Chertkov had concealed his "insurance" during his wartime escapades. The Russian unwittingly holds key evidence to several mysteries, but their solutions require additional data from an aging survivor of the wartime Resistance.