The Untouchable, 1998, by John Banville.
A brilliant, engaging, and highly literate espionage-cum-existential novel, John Banville's The Untouchable concerns the suddenly-exposed double agent Victor Maskell, a character based on the real Cambridge intellectual elites who famously spied on the United Kingdom in the middle of the 20th century. But Maskell--scholar, adventurer, soldier, art curator, and more--respected and still living in England well past his retirement from espionage, looked like he was going to get away with it when suddenly, in his 70s and sick with cancer, he is unmasked. The question of why, and by whom is not as important for Maskell as the larger question of who finally he himself really is, why he spied in the first place, and whether his many-faceted existence adds up to an authentic life. (Amazon.com Review)