Mary Welsh, a celebrated wartime journalist during the London Blitz and the liberation of Paris, meets Ernest Hemingway in May 1944. He becomes so infatuated with Mary that he asks her to marry him the third time they meet—although they are married to other people. Eventually, she succumbs to Ernest's campaign, and in the last days of the war joined him at his estate in Cuba.

Through Mary's eyes, we see Ernest Hemingway in a fresh light. Their turbulent marriage survives his cruelty and abuse, perhaps because of their sexual compatibility and her essential contribution to his writing. She reads and types his work each day—and makes plot suggestions. She becomes crucial to his work and he depends upon her critical reading of his work to know if he has it right. We watch as they travel to the ski country of the Dolomites, commute to Harry's Bar in Venice; and attend bullfights in Pamplona and Madrid. We see Ernest fall in love with a teenaged Italian countess and wonder at Mary's tolerance of the affair. We witness Ernest's sad decline and Mary's efforts to avoid the stigma of suicide by claiming his death was an accident.

Her story is one of an opinionated woman who smokes Camels, drinks gin, swears like a man, sings like Edith Piaf, loves passionately, and experiments with gender fluidity in her extraordinary life with Ernest.