Death in Vienna by Daniel, Silva

Art restorer and spy Gabriel Allon is sent to Vienna to discover the truth behind a bombing which killed an old friend - a Nazi hunter. While there he encounters something that turns his whole life upside down. Each fact he uncovers only leads to more questions until finally a picture emerges which is more terrible than he could have ever imagined - a portrait of evil stretching across 60 years and thousands of lives into his own personal nightmares.