If your husband was Ernest Hemingway, would you invite his lover along on your family vacation? Hadley Richardson, the first Mrs. Hemingway, made that choice in the summer of 1926, asking Pauline Pfeiffer (known as Fife) to join the couple in Antibes, though she recognized her elegant rival's "rich woman's sense of entitlement: of deserving a particular object only by virtue of desiring it, whether it was a bicycle or a Schiaparelli dress or another woman's husband." Why did she take that risk? In her magnetic novel about Hemingway's four dramatically different wives, Wood suggests that Hadley intended to force a crisis. "I want to know if it's her or me," she tells "darling Ernest" before they head to a party where the other woman will upstage her. Fife became the author's next wife, but she wouldn't be his last. Hemingway's compulsion for variety was matched by his hunger for domesticity. "Marriage is excellent for me," he tells his strong-willed third wife, Martha Gellhorn (whom he once sent a cable that scolded: "are You a War Correspondent or a wife in my bed?"). After that marriage exploded, he married the fourth - and final - Mrs. Hemingway, Mary Welsh, a gentler journalist. Spanning almost four decades, touching down in France, England, Spain and the Americas, Wood's novel assembles a satisfying puzzle of personalities, bringing each relationship's beginning, end and overlap into vivid focus. "Ernest had, by default, to be shared," Mary Hemingway reflects in Idaho in 1961, soon after his death. "The thing was not to be heartbroken about it." LIESL SCHILLINGER, a regular contributor to the Book Review, is the author of "Wordbirds."