Maurice Castle is a high-level operative in the British secret service during the Cold War. He is deeply in love with his African wife, who escaped apartheid South Africa with the help of his communist friend. Despite his misgivings, Castle decides to act as a double agent, passing information to the Soviets to help his in-laws in South Africa. In order to evade detection, he allows his assistant to be wrongly identified as the source of the leaks. But when suspicions remain, Castle is forced to make an even more excruciating sacrifice to save himself. Originally published in 1978, "The Human Factor "is an exciting novel of espionage drawn from Greene's own experiences in MI6 during World War II, and ultimately a deeply humanistic examination of the very nature of loyalty. This edition features a new introduction by Colm Toibin.