• Fiction. By Lionel Shriver. HarperCollins, $25.95.Grade: A-

Plot in a nutshell: One fateful night in July, Irina McGovern, an American ex-pat in London, finds herself in a breathtaking dilemma. She is suddenly, overwhelmingly attracted to Ramsey Acton, a famous British snooker player. If she kisses him, it will destroy her 9-year relationship with her solid and loving partner, Lawrence Trainer. But if she doesn't, she might always regret it.

Shriver, the celebrated author of the novel, We Need to Talk About Kevin, takes this dilemma and runs with it. She builds the tension in the first chapter, ending the moment before Irina makes her decision. Shriver then follows Irina's life first as if she had kissed Ramsey, and in alternate chapters, as if she had chosen not to kiss him.

The choice, which lasts only a second, has profound reverberations either way. Ramsey and Lawrence are diametrically opposed: Ramsey is sexually charged and emotionally difficult. Every night is filled with extravagant restaurants, cognac, cigarettes, and snooker matches. Lawrence, on the other hand, works at a prestigious London think tank and gives dry lectures on Northern Ireland. He provides Irina with a seemingly secure, orderly life.

Shriver doesn't deign to write a "good choice vs. bad choice" novel, however. Both choices have intense repercussions and both leave Irina questioning her decision.

Sample of prose: "Irina had only seen Ramsey play on TV, and in three dimensions the twelve-by-six-foot table yawned much larger than it appeared on screen. Up close, the accuracy of the shots, the surety of their selection, and the unearthly precision with which every pot set him up for the next ball seemed inhuman. As he swung from shot to shot, Ramsey's black silk jacket wafted in the breeze from the upper windows."

Pros: The scenes with Ramsey are spectacular, especially an encounter with Irina's rigid, controlling mother. Ramsey swoops in like a bad-boy knight-in-shining-armor. The Ramsey chapters, in fact, could comprise a riveting novel on their own.

Cons: The chapters about Lawrence drag in comparison. The dramatic tension just can't compete.

Final word: Refusing to indulge in "happily ever after" fantasies, Shriver has created an adult choose-your-own-ending book, with fascinating results.