Why not “cruise Cézanne country” in the fall? he suggested.

Mary liked the idea very much. It had not been easy to adapt to a life in the tropics as the new Mrs. Hemingway. A trip to Europe would be good for them. They could take their royal blue Buick roadster over to France and hire a chauffeur to drive them around.

Down at Havana’s harbor, Mary fell for the Jagiello, a sturdy German-built ship awarded to Poland after the war and based in Genoa. On board she found Polish officers and an Italian crew. “It is clean, airy, cheerful, apparently solid and good in any sea,” she reported. The ship was on its way to Europe but would be back at the end of the summer. The timing was perfect. Captain Jan Godecki, a friendly chap with a smooth round face and a sharp nose like Pinocchio’s, agreed to haul the big Buick onto the foredeck, and the deal was sealed.

On September 6, 1948, the Hemingways bade farewell to the staff at Finca Vigía, their rambling stucco house in the village of San Francisco de Paula, and drove down to the port of Havana with thirty-some pieces of luggage. Their closest Cuban friends and a few diplomats from the U.S. Embassy joined them at a small farewell party aboard the ship. John Dos Passos was also there. He and Hemingway had had a falling out at the time of the Spanish Civil War—Hemingway accusing his old friend of betraying the Loyalist cause out of political naïveté. They hadn’t seen each other in years when Dos called out of the blue to say he was in Miami and could he come over to visit. It was really not a good time. The boat was leaving in three days, and the Hemingways were packing and making last-minute arrangements. But Dos came over anyway, and he and Hemingway had a long talk over drinks at the Finca. Though it didn’t really fix things between them, they shared memories of the good times they had spent together in the twenties in Paris, Pamplona, Gstaad, and the south of France, where the Hemingways were now headed.

After a final round of abrazos, the guests disembarked and the Jagiello was finally off. Horns blew in the harbor, and paper streamers flapped and fluttered in the breeze. At the bow, tightly fastened to the deck, the blue Buick gleamed like a captive mermaid.

They slept like logs. The only complaint was the defective toilet in their cabin, a “shit-spitting dragon” that was best left unflushed.

To keep herself busy, Mary edited the ship’s daily news bulletin and read it out over the loudspeaker. Ernest liked to gather a little crowd of passengers and crew on the upper deck to give his wife a round of applause at the end of her newscast. He was in a good mood and very gregarious; he enjoyed being Chief Entertainer on board.

The Hemingways had plenty of time to study and read. Mary, ever the disciplined traveler, brushed up her French. Ernest plowed through Isabel and the Sea, an account by his friend George Millar, a former British officer turned farmer, about his boat trip down the canals of France. He found the book a little tiresome, but Millar’s descriptions of la France profonde were vivid enough to bring back pleasant memories of his time in France.

The Hemingways hadn’t planned an itinerary. They would take it day by day, driving through Provence and slowly making their way north to their final destination: the Ritz in Paris, where they had fallen in love four years earlier, during the last stages of the war.

Hemingway was very insistent from the start. He told Mary he wanted to marry her the same day her former beau, Irwin Shaw, introduced him to her at the White Tower, a fashionable London restaurant. “Don’t be silly,” she replied. “We are both married and we don’t even know each other.” But he continued to press his case, first in London and later in Paris, where they spent happy, exhilarating times at the Ritz. Mary fell in love with him and eventually moved into his room—Chambre 86. Her husband, conveniently enough, was in Southeast Asia, reporting on the Allied counteroffensive against the Japanese.

At the end of the war, Hemingway went back to Cuba and asked Mary to join him. She went for a clean break: gave up her career, divorced Mr. Monks, and sailed to Havana. It was a startling decision for such an independent woman, and she knew from the beginning that she would have to devote herself entirely to her husband to make the marriage work. But it was what she wanted.

They were married in Havana as soon as their respective divorce papers came through. Mary did her best to settle in at the Finca, which Hemingway had bought in the late thirties at Gellhorn’s urging, and which was still full of her things. But adjusting all at once to Hemingway’s house, his friends, his life had been harder than expected. She missed her smart, sophisticated friends in London and Paris. Drinking rum with her husband’s local pals and shooting pigeons at the Club de Cazadores down the road was not her idea of fun—especially when they ran out of pigeons and started shooting oyster shells and crabs.

There was also the question of children. Hemingway already had three sons. John, the eldest, was by his first wife, Hadley Richardson; he was twenty-five and a young career officer in the U.S. Army. Patrick and Gregory, seventeen and fourteen, were by his second wife, Pauline Pfeiffer, who lived with the boys in the family house in Key West. Mary was thirty-seven when she moved to Cuba, and eager to have a child of her own.

Hemingway was not enthusiastic about becoming a father again, but when Mary became pregnant a year into the marriage, he warmed to the idea of having another child, especially a little girl. In their late-night conversations, they agreed to call her Bridget.

In late August 1946 they took the car over to Florida and drove to Idaho for the winter season. On the way out, in a motel room in Casper, Wyoming, one of Mary’s fallopian tubes ruptured—it turned out she had an ectopic pregnancy. She lost the child, suffering atrocious pain, and came very close to losing her own life on the operating table of the small-town hospital.

In the spring of 1947, Mary had barely recovered from the physical and emotional trauma of her miscarriage when life at the Finca was again thrown into turmoil. Young Patrick, who was staying with them while he studied for the college boards to gain admission to Harvard, went over to Key West to be with his younger brother during Gregory’s spring break. Gregory, who had a reckless streak, crashed the car; he was under age and driving without a license. Patrick was with him. He hit his head and suffered a severe concussion. But it was only once he was back at the Finca that the effects of his head injury manifested themselves. He drifted into a state of increasing confusion and eventually had a complete breakdown. Bedridden for weeks, he moved in and out of consciousness. Hemingway kept vigil at his son’s bedside, sleeping on a mattress; Pauline flew over from Key West.

Mary, meanwhile, traveled to Chicago to assist her father, stricken by prostate cancer.

“Longing for the day when we can get back to our own fine life,” she wrote to her husband. But after more than a year of marriage it sometimes seemed to Mary that her life with Hemingway hadn’t properly started.

Patrick recovered over the summer, took his exams, and was accepted at Harvard. Life gradually returned to normal. To celebrate the end of the ordeal, Hemingway bought the Buick, with its fine red leather seats, and drove it out to Sun Valley in the autumn. Mary joined him, and they spent the winter in a rented cabin in Ketchum. While Hemingway worked every morning, Mary took her first skiing lessons on Dollar Mountain and embraced the sport with enthusiasm.

At the end of the winter, they returned to Cuba. They were seldom alone. Guests were always passing through. Meals were often crowded. There were also fine fishing trips along the coast of Cuba on the Pilar, Hemingway’s beloved boat. And Mary was excited about the new lookout tower they were building next to the main house. But managing the household while at the same time making sure all her husband’s needs were tended to was a tiring occupation that afforded little gratification. “With so many friends to entertain and amuse,” Mary later observed, “he simply didn’t see me in the landscape. I did not like it but I could not invent a situation which would correct it.”

Hemingway’s frustration with his writing made it even harder for Mary to get along with him. This was an especially challenging time in his career: not yet fifty, he was already having to stare back at his long-established canon, which included his three classic novels—The Sun Also Rises, A Farewell to Arms, and For Whom the Bell Tolls—and of course the short stories. Soon after his return from the European theater of war, he had embarked on an ambitious project: a monumental trilogy about the war by air, sea, and land. By the early summer of 1948, he had over nine hundred pages in longhand. But he was struggling to give the book a proper shape, and the writing did not satisfy him. He knew what the critics in New York were saying: he was a writer of the past, and his best stuff was behind him. So he was determined to write a really big book. Big enough and good enough to beat back the young writers who had come out of the war. In May of that year, Norman Mailer, the twenty-five-year-old wunderkind of the American literary scene, had published his war novel, The Naked and the Dead. It had rocketed up to the number-one spot on the New York Times Best Seller List. And there was talk of another big war novel soon to be out: The Young Lions, by none other than Mary’s ex, Irwin Shaw.

Back in the spring of 1944, Hemingway had just walked away from their table at the White Tower when Shaw had turned to Mary and said, “Well, it’s been nice knowing you.”

“You off somewhere?”

“A monopoly has just been born, you dummy.”

“You’re off your rocker.”

But Shaw had been right. There she was, four years later, living in Cuba and still struggling to find her proper place in the Hemingway “monopoly.” So, when her husband came up with the idea of a trip to France, she did not let the opportunity slip by.

There was only one incident during the en...