The Innocent by David Szalay
It is 1948 and Aleksandr, a major in the MGB (the forerunner of the KGB) is sent to an isolated psychiatric clinic to investigate one of the patients there. The patient is a man long presumed dead - a now severely incapacitated veteran of the Second World War, who seems unable to remember any of his past. Twenty-four years later, Aleksandr is haunted by the case. With his Stalinist faith under threat as the Cold War recedes, he interrogates his memories and the effect the case had on himself and on those he loved most.