When he joined Britain’s overseas-intelligence service, M.I.6, under the guise of entering the Foreign Office, David Cornwell wrote to his adored stepmother, Jeannie: “I shall have to go to a charm school.” In truth, there were no worries on that front: the man who would write under the name John le Carré had graduated from such institutions with highest honors years before.

It’s no coincidence that he kept sending lovingly intimate letters to his stepmother even as he seldom, one senses, corresponded with her notoriously shifty husband. Le Carré was haunted all his life by the wish to maintain as much distance as possible from his con-man father—and by the fear that he might well be something of an irresistible dissembler, a spinner of fictions, himself. As his housemaster at boarding school observed of the 16-year-old who suddenly took off for Switzerland, “He strikes me as the sort who might become either Archbishop of Canterbury or a first rate criminal.”

It’s open season this year on a notoriously private master of intelligence who thrived by keeping to himself. One ex-mistress has published a breathless account of ice-cube-enhanced sex with the compulsively elusive soul she refers to as “an enigma machine”; her lover’s biographer, Adam Sisman, reports uncovering at least nine other le Carré mistresses in all.

None of this would have been welcome to a dashing escape artist who, almost 30 years ago, scared off one would-be biographer with a lawsuit. No sooner had Sisman brought out his not-quite-authorized biography, in 2015, than le Carré struck back with a flare of diversionary memories, The Pigeon Tunnel. Now, two years after the author’s death, his third son, Tim (who suddenly collapsed and died as he was putting his finishing touches on the project), has assembled some of his father’s largely handwritten letters in a volume of 663 pages, to be published next week, that includes “only a smattering of letters to his lovers, of whom there were quite a few.”

That absence is felt on every page of a brisk and sometimes cursory survey of career highlights. Yet le Carré could never be anything but fluent, persuasive, and fantastically entertaining. We see him here tossing off cartoons of birds (and deft caricatures of himself); composing a many-paragraphed thank-you letter for some hand-embroidered napkins; advising a 10-year-old boy who wants to become a spy.

Wooing Alec Guinness to keep acting as George Smiley in a TV adaptation of one of his books, le Carré is effortlessly brilliant and perceptive; with old schoolmates, he’s larkish and self-deprecating, inviting them to his “schloss” (so long as they keep to themselves while he’s at work). As Tim Cornwell notes in his fond and discerning introduction, a volume of P. G. Wodehouse was the only book his father took to the hospital before he died. And—as all his readers know—le Carré could write with the urbanity of a British gentleman precisely because he wasn’t one.

The letters also, however, remind us of the moral rage just behind the silky surface. Advising Sydney Pollack about a planned film adaptation of his 1993 novel, The Night Manager, le Carré tells the seasoned director not to go light on the book’s righteous indignation.

Here is a man—a “secret pilgrim,” as he titled one of his books—who really did spend a week seeking absolution at an Anglican monastery and even in later years signed off with “God bless.” Part of the poignancy—the power—of le Carré is that he couldn’t believe in king and country, but he longed to believe in something. He always had a keener sense of what he could see through than of what he could have faith in. That sense of distrust extended even to himself—Sisman’s biography, he initially hoped, could offer “a gift of truth, of a sort, to my children, & one I could never hope to deliver myself.”

In one celebrated exchange with Salman Rushdie soon after the fatwa was declared—le Carré found Rushdie “a victim, but in my book no hero”—the often disenchanted novelist protested, “I don’t think there is anything to deplore in religious fervour.”

Le Carré refers to an East German spy serving “a disgusting regime in disgusting ways,” but that did not mean he loved either Washington or Whitehall. His contempt for the traitorous Kim Philby (deformed, le Carré felt, by a roguish father) led to a temporary falling-out with Graham Greene, subject of some of the most intriguing letters here. Connoisseurs of coincidence might relish the fact that one of le Carré’s “life-long secret sharers” was a reverend called Vivian Green, who lived in Oxford, not far from Graham Greene’s long-abandoned wife, Vivien Greene.

In life as in art, le Carre’s weak spot would always be affairs of the heart; his master spy, Smiley, can solve everything except his wife. Here we do get a frantic love letter to the writer’s well-known mistress Susan Kennaway, which offers a glimpse of the romantic who chose to live under deepest cover, otherwise known as his books. We also get the curiosity of a love letter to his second wife, Jane, nearly 15 years after they were married. Yet le Carré remains so furiously eloquent even in his passion that one can’t help wondering whether the first billet-doux isn’t a kiss-off and the second an oblique apology.

We’ll never get to the bottom of this man of layers and borrowed voices, and it’s not clear that he ever did, either. We see him here sounding most personal when he describes one of his protagonists as “at heart a monk, a mountain climber, a solitary soldier, a watcher, and a person of determined solitude and self-sufficiency, even though he longs to connect.” A world-class mimic at the dinner table, the author of 27 books chose to live six hours by car from London, maintained few friendships, and never learned to type (that task was left to his wives). Tremendous company, the letters remind us, even when he was giving next to nothing away.

A Private Spy: The Letters of John le Carré, edited by Tim Cornwell, will be published by Viking on December 6

Pico Iyer is a Columnist for Air Mail. His new book, The Half Known Life: In Search of Paradise, will be published by Riverhead on January 10