Or how, in the face of these internal and external difficulties, he continued to produce outstanding work. In 1962, he wrote a long article for The New Yorker called “The Edinburgh Caper”; it was published as a book the same year with the subtitle “A One-Man International Plot.” It bears some similarities to the Guam piece, but there, McKelway had a reasonable belief that, in his mind, grew way out of proportion. Here, he takes us step by step through the development of a paranoid delusion. Specifically, while on a trip to Scotland three years earlier, he imagined that he was involved in CIA skulduggery intended to foil a Soviet plot to kidnap Queen Elizabeth and President Eisenhower. Among other things, he fancied he was being sent messages by means of the letters and numbers on the license plates of passing cars. Even more so than in the Guam article, McKelway’s description of the onset and development of the delusion is compelling because it is so matter of fact. Waking up in his hotel room in Edinburgh, he writes,

a jumble of disturbing thoughts flashed through my head with great rapidity … . I thought of the Camerons [a pleasant Scottish couple he had befriended] as being somehow menacing. In short, I hated them. It is only to those we love that we turn at unexpected times the gnarled and ugly face of hatred. And in that realm, suspicion readily moves into the space close to our hearts that we thought could be occupied only by trust. These thoughts of mine, you understand, came into my head with terrific speed and were gone in a few seconds, but in those few seconds, I saw Cameron as a Soviet agent of the highest type, and Mrs. Cameron as a co-agent.

He ends up standing outside the hotel where an American officer is staying and — having gotten it into his head that this is the expected means of communication — singing excerpts from an Ethel Merman song at the top of his lungs. Not surprisingly, he is arrested, and in his jail cell, in addition to continuing with the Merman song, he shouts out “such phrases as ‘Now the Labradors. And now the setters and pointers. And here come the weimaraners.’ These seemed to me to represent the different types of Strategic Air Command bombers that were on their way to the rendezvous over Russia.” He ends up finding and confiding in the officer, but it turns out the colonel has been in touch with Curtis LeMay, knows all about the “ Guam caper,” and receives McKelway’s allegations in good humor. By that time, the writer’s cooler heads are prevailing, and he quickly wraps up loose ends. More than four decades later, “The Edinburg Caper” remains a unique and riveting work of interior journalism: a book resembling what Joseph Mitchell’s Joe Gould’s Secret might have been had it been written by a lucid Joe Gould.

McKelway had about ten years of lucidity left. He wrote one more New Yorker fact piece (a long profile of the greatest impostor in New York history) and more than a dozen elegiac reminiscences and lightly fictionalized sketches describing his early life in Washington, New York, and Bangkok. They included two short stories, “First Marriage” and “The Fireflies,” that Shawn described as “among the loveliest the magazine ever published.” The manic or delusional episodes became more frequent; according to Roger Angell, “he would go off his medication because he wanted to experience the highs.” But he carried them off with style. The late New Yorker editor Robert Bingham told Calvin Trillin, who joined the staff in the sixties, of being summoned one Sunday to the Plaza Hotel, where McKelway was making a scene. “Mac had taken a cab to the Plaza, in his pajamas,” Trillin says. “When Bob got there, Mac was being obstreperous. The kindest New York cop you’d ever seen was saying, ‘Mr. McKelway, why don’t you sit down? You’ll be more comfortable.’ And Mac said: ‘Don’t try any of your Gestapo tactics on me!’”

At one point, he started scribbling meaningless words and doodles on the eighteenth-floor walls of the New Yorker offices. He even got some cartoonists to contribute. “Soon there was an area about fifty feet across, full of graffiti,” Trillin says. “I walked in one day and the receptionist told me, ‘You may have a problem getting in your office. They’re painting.’ I said, ‘Didn’t they paint six months ago?’ She said, ‘Don’t you understand? They’re getting rid of Mr. McKelway’s wall without hurting his feelings.’”

Ben Yagoda directs the journalism program at the University of Delaware and is the author of About Town: The New Yorker and the World It Made and When You Catch an Adjective, Kill It: The Parts of Speech, for Better and/or Worse, which will be published by Broadway Books in February.