If Marilyn Monroe’s first husband James Dougherty—the only unknown in a string of infamous lovers, the only one who fell for the actress when she, too, was an unknown—had spent the rest of his life loving her, chasing her, trying to tame her after she’d left him, his memoir would have read like Mario Vargas Llosa’s new novel, “The Bad Girl.” While Marilyn is probably the original Bad Girl, the novel’s titular bad girl is no less a seductress, adventure-seeker, or opportunist than the actress was thought to be, although hers is a less intriguing and iconic story.

Otilita—we learn this is her given name only in the last fifty pages of the book—first appears as Lily, an exotic Chilean schoolgirl who captures the hearts of her upper-class Peruvian classmates, including the protagonist Ricardo, who is known throughout the book as “good boy.” When she disappears after she is discovered to be neither Chilean nor upper-class, Ricardo, already lovestruck at the ripe age of fifteen, fears he will never see her again. But he does, and often; as Comrade Arlette, a guerrilla fighter being trained by the Cuban revolutionaries; as Madame Robert Arnoux, the wife of a French bureaucrat; as Mrs. Patricia Robinson, the wife of a British racetrack regular; as Kuriko, the mistress of Japanese mobster; as Lucy, a broken woman.

Vargas Llosa has worn many hats himself, from a prominent Latin American intellectual who hob-nobbed with the likes of Castro and Garcia Marquez to a one-time Peruvian presidential candidate, from a literary critic to a novelist and later a professor, from the husband of his aunt to the husband of his cousin. A sometime resident of Bolivia, Peru, Spain, France, and the United States, Vargas Llosa’s life has been, in many ways, as cosmopolitan and as diverse as the Bad Girl’s is.

Indeed, it is the book’s cosmopolitanism that fills out the rather bare plotline and gives it a modern, worldly shape. Each episode between the good boy and the bad girl is unique only because of the backdrop on which it takes place, whether they’re among postmodern intellectuals and would-be revolutionaries in France or smugglers pushing illegal substances in Japan. All of the characters in the book are well-read, well-traveled, and well-aware of the perils of the twentieth-century lifestyles they lead. In that sense, the underlying theme of despair is in almost every paragraph, even the ones that catch Ricardo and his bad girl at a truce. There is a suggestion that the abnormality of their relationship is merely a particular strain of a disease we’ve all caught, a suggestion that the unconventional is today’s norm.

But “The Bad Girl” is still a love story, though it would be better characterized as a story of obsession. Each time he sees her, though years may pass in between their flings, Ricardo professes his undying love for this woman who has no regard for his feelings and who shamelessly uses his affections for her own ends. After one of her many abrupt departures from his life, Ricardo finds a toothbrush she has left behind in his apartment and experiences a visceral agony comparable to the withdrawal of an addict: “I was in a sweat all night, my mind blank, as I clutched the Guerlain toothbrush that I kept like a charm in my night table, chewing on my despair and jealousy. The next day I was a wreck, my body shaken by chills, without energy for anything, and I didn’t even want to eat.”

As with any love story, the ending makes or breaks all: Will they get together? It is here that Vargas Llosa’s train runs out of steam. For such an unconventional story with such unconventional characters, the ending is painfully banal: the bad girl returns to her schoolboy sweetheart. The bad girl-turned-good ending is wholly uncompelling. “At least admit I’ve given you the subject for a novel. Haven’t I, good boy?” Otilita tritely says at the end. Perhaps she has, but, in her movie-ending change-of-heart, she has also done away with the darker edge that made the novel worth reading.

—Staff writer Anjali Motgi can be reached at amotgi@fas.harvard.edu.