The only novel that LeCarre has written outside of the espionage genre, The Naive and Sentimental Lover is an exploration of the nature of love and obsession. The main character, Aldo Cassidy, is a stolidly successful businessman. When he goes to Somerset to look at house he is considering buying, he meets a couple who are squatting there: Shamus and Helen.

Shamus is emerging as a successful novelist, while Helen's main attribute is her beauty. In a complete reversal of his usual obedience to the mores of society, Aldo falls in love with them both. While he is under their spell, he becomes enchanted with a way of life that is very different from his own.

LeCarre wrote this book after the breakup of his first marriage. There is some evidence to indicate that it is at least in part autobiographical. Although it is a departure from his usual backdrop of the world of spies, this novel explores many of the same interior themes, and stands alone as the work of a masterful writer.