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The Human Factor (original 1978; edition 1978)
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Wikipedia in English (1)
Maurice Castle is an aging bureaucrat in the British secret service MI6. Married to a black African woman with whom he fell in love during his previous stint in apartheid South Africa, he now lives a quiet life in the suburbs and looks forward to retirement. As the book begins, however, a leak has been traced to the African section in London where he works and threatens to disrupt this precarious tranquility. Castle and younger colleague Davis make light of the resulting inquiry, but when Davis is accused on circumstantial evidence and quietly "disposed of", Castle begins to wrestle with questions of loyalty, morality and conscience. On the one hand, Castle undertakes his day-to-day job professionally, and is willing to do what is more than required for both Davis and Daintry, his boss. On the other hand, Castle is grateful to Carson, who, as a Communist, has helped Castle's wife escape South Africa. In return, Castle decides to help the Communists and believes that by helping them, he is helping his wife's people -- not knowing that Moscow has all along been using him for entirely different purposes.
(summary from another edition)