I loved An Officer and a Spy by Robert Harris. It is a historical and fictionalized account of the Dreyfus affair, the shameful anti-Semitic affair in which a Jewish army officer, Alfred Dreyfus, was unjustly accused and convicted of espionage. Harris makes his protagonist a young intelligence officer named Georges Picquart, and follows him as he slowly uncovers the truth about Dreyfus and the massive military and intelligence apparatus that convicted him. It is masterfully done, staying close and revealing, in a truly historical way, the historical sources themselves. And it’s an absolutely riveting read, at once a mystery and a thriller.