I do not, as a rule, rummage in people’s desk drawers. In the checkout line at the supermarket, I rarely succumb to the temptation to have a quick read about Nicole Kidman’s latest heartaches. But when I learned recently that Graham Greene’s letters to his lover, Catherine Walston, were available for inspection in the Special Collections department of the GeorgetownUniversity library, my resistance failed. I had to see them.

My curiosity, I rationalized, was not so much prurient as literary. Greene was one of the greatest writers of the past century. His affair with Walston began when he was working on what became, in my judgment, his best novel, The Heart of the Matter. It continued through the writing of The End of the Affair, which was almost as good. Greene’s biographers have written about the letters, and I wanted to see them for myself. They might, I thought, illuminate the osmotic border between his fiction and his life.

They are kept, it turns out, in dozens of stiff, slender cardboard boxes, each the pale gray color of a London sky. Inside each box are about 30 green folders and in each folder is a letter, or a postcard, perhaps a photograph. A polite, well-scrubbed graduate student brought me the first box, and I opened the first folder. I found a letter postmarked London, 25 September 1946, 6:15, written on a flimsy sheet of paper with the letterhead "Eyre & Spottiswoode, (Publishers) Limited." Seeing Greene’s handwriting, created in evident haste with a fountain pen, I felt at first as if I were handling a relic. Then I was struck by a sense of mortality. In these boxes were the remnants of a passion that consumed two remarkable human beings.

"Dear Mrs. Walston," the first letter begins. Greene’s hand is barely decipherable. He wrote as if he had no time to waste forming vowels. His consonants were spare as spiders’ legs. "I feel I am a most neglectful god-father! I haven’t even sent you a silver mug or a spoon to bite."

That was the genesis of the affair. Catherine Walston was the American-born wife of a wealthy British land-owner. At the age of 30, inspired by Greene’s work (he had published a novel about a martyred Mexican priest, The Power and the Glory, in 1940), she decided to convert to Catholicism. Though she had never met Greene, she asked him to be her godfather. He accepted, but could not attend the ceremony. He sent his wife, Vivien, in his place. A polite friendship between families developed, but within a few folders, it becomes increasingly clear that the friendship quickly led to the affair.

In one letter, Greene refers to the precise instant this happened for him. It was in a small plane chartered by Mrs. Walston to take him home to Oxford after a winter afternoon at her estate. "A lock of hair touches one’s eyes in a plane with East Anglia under snow," he wrote, "and one is in love."

The affair would go on for many years—in London, in Capri, in Ireland, in Paris. Greene had been more or less separated from his wife when it began, and shortly thereafter he left her formally. He was also still involved with his wartime mistress, Dorothy Glover. His personal life, as he acknowledged to Walston more than once, was rather grotesquely complicated.

Hers was no less so. Greene was not her only lover. Some of Greene’s love letters are written on the stationery of her husband’s estate, Thriplow Farm, and refer to trysts that took place while he was a guest in her house, ostensibly visiting not only her but her husband and her children. Harry Walston evidently did not interfere in his wife’s personal life until the affair with Greene became a matter of widespread gossip.

Greene’s character emerges quickly in the letters. He wrote to her about his conscience, about the way he rationalized the affair, about his dreams. Reporting on an evening’s slumber in the spring of 1949, he sent her what could well serve as his epitaph: "I woke up this morning very calm and quiet... after an odd dream of being dead, but even dead there were women and bedrooms." Thoughts of death and thoughts of women were forever rivals in his mind.

The reader of the letters perceives Walston only indirectly. Most of the correspondence Greene received from her he destroyed. Her thoughts are revealed only in Greene’s responses, her actions only in his reactions.

She was a striking woman. In a photograph in the collection, she is dressed in what appears to be a linen pantsuit. She has short, slightly curly hair, full lips, fine features. Her hands are elegantly manicured, her nails painted. She is smoking a cigarette, as she often was when she was photographed. It seems in these times to convey a self-destructive urge, though in her time it may only have suggested sophistication.

But it was evidently not only her looks that attracted Greene. What seemed to have fascinated him was the combination of her carnality and her Catholicism. Like him, she took her adopted faith seriously, in her own fashion. Like him, she seemed to be able to live with one foot in the sacred world and one foot in the profane. His letters to her reflected both spheres. Sometimes he spoke of missing her at Mass, of remembering her in his prayers, and closed with "God bless you." The next day he might close, in code decipherable by any lust-struck boy: "I.W.T.F.Y."

"I love onion sandwiches. G.," Greene wrote cryptically in March 1947, on a postcard from Amsterdam. With this card, the line between fiction and life begins to blur. Maurice Bendrix, the narrator of The End of the Affair, falls in love with Sarah Miles over a dish of onions at a restaurant called Rules. Evidently, onions had a special meaning for Greene and Walston as well. It was one of their code words for making love.

The onion postcard is one of many things in the correspondence that make clear how much Greene lifted from his life and inserted more or less whole into his novels. It struck me that Walston served as a model for both Sarah Miles and Helen Rolt, who becomes Major Scobie’s lover in The Heart of the Matter. Like Catherine Walston, Sarah Miles had a husband whom she respected but no longer desired. Like Walston, she wrestled with the contradictions between her religion and her passion. Like Scobie, Greene had a wife whom he no longer loved and a conscience that periodically cast him into a slough of despond.

Sometimes in these letters it’s not clear whether art imitates life or the other way round. In April 1950, Greene wrote to Walston that he had gone to confession and told the priest everything. The priest had replied that if he wished absolution, he must stop seeing Walston and go back to his wife. "I’m sorry," Greene had replied. "I’m afraid I must find another confessor." It was almost a verbatim duplicate of a fictional attempt at confession he had written for Major Scobie, a scene that was published in 1948.

I had expected to feel some irony as I read the letters, an irony rooted in the fact that someone who flouted so many tenets of Catholicism should ultimately have his letters preserved in a Catholic university. Instead, I found myself understanding why Georgetown paid a reported $150,000 for the letters when Walston’s heirs put them up for sale in 1990. Though he failed in many ways to meet the standards of his faith, Greene never committed the transgression of taking it lightly. He might not always have been a good Catholic, but he was always a serious Catholic.

He seems to have reached for Walston not just for the simple pleasure of the affair but for the way it fertilized his imagination. "I believe I’ve got a book coming. I feel so excited," he wrote in the autumn of 1947. "Tonight I had a solitary good dinner where I usually go with My Girl [erstwhile mistress Dorothy Glover] and afterwards felt vaguely restless (not sexually, just restless) so I walked to the Café Royal and sat and read...and drank beer till about 10 and then I still felt restless, so I walked all up Piccadilly and back... suddenly...I saw...the beginning, the middle and the end and in some ways all the ideas I had.... I hope to God it lasts—they don’t always." He concluded with a triumphant postscript: "I’m not played out yet!"

As an occasional novelist myself (though one likely to be spoken of in the same breath as Greene only by people who read this essay aloud), I found the differences between the reality depicted in the letters and the world of the novels to be more instructive than the similarities. Greene knew how to make his characters more sympathetic than he himself was. Both he and Scobie, for instance, fell out of love with their wives and had affairs. But Scobie committed suicide rather than cause further pain to his wife. Scobie’s creator might have agonized for a while, but he was able to move his wife and children to a cold spot in his heart. Late in 1947, he wrote to Walston of "a sudden feeling of indifference about poor Vivien. A feeling that I’ve done all the worrying of which I’m capable."

The affair reached its apogee in the late 1940s. By 1950, Greene was begging Walston to leave her husband and marry him. She declined, for reasons the letters only hint at. Perhaps she was afraid she would lose her children in a custody battle. Perhaps she opted for the security of life with a rich and indulgent man. Perhaps she realized that Greene’s habits and temperament were better suited to a lover than a husband.

The affair cooled, though Greene wrote to her until she died in 1978, still the wife of Harry Walston. Greene had other women and wrote other books before he died in 1991. None of the subsequent books, I think, probed as deeply as the work she inspired. Though he remained on friendly terms with Walston, I suspect he saved his true response to her rejection of his marriage proposal for The End of the Affair. In its concluding stages, Sarah Miles dies.

Strangely, though, I returned the last box feeling rather less like an invader of privacy than I had when I started. "The act of creation is awfully odd and inexplicably like falling in love," Greene wrote in one of his early letters to Walston. That may be true, but when I finished reading the record of Greene’s great love, I felt like a spectator at the coronation of the Japanese emperor. That essential moment of communion between the emperor and the sun is screened and unseen. So, too, must be the moment of creation when a writer like Greene takes the stuff of these letters and turns it into fiction. The secret of that trick is a matter whose privacy Greene maintains in his grave.