Two-timing

The Post-Birthday World
By Lionel Shriver
HarperCollins, 517 pp., $25.95

An acquaintance of mine once took pains to depress me by explaining in ghoulish detail how life was a series of missed chances and wrong-headed choices. Every day, she insisted, we were making decisions, and the result was what she referred to as a winnowing of life's opportunities. One small choice could change absolutely everything.

Such is the premise of Lionel Shriver's new novel, "The Post-Birthday World." Irina McGovern, an American children's book illustrator living in London, is happily involved with a dependable if not especially passionate think- tank wonk named Lawrence Trainer, also an American. The two have been living together for nearly a decade, when suddenly she is faced with a pivotal, life-altering choice:

"It could have been a small decision. Drunken, addled revelers often do things late at night for which they apologize in the morning with a reductive titter. But the minimizing of such moments was a matter for other people. For Irina knew with perfect certainty that she now stood at the most consequential crossroads of her life."

The choice? Should she kiss British snooker celebrity Ramsey Acton as the two of them are alone by the snooker table in his townhouse? Or should she resist, despite the profound desire she suddenly feels to be in the man's arms?

Snooker, Shriver teaches us, is a British version of pool that is immensely popular in the United Kingdom. "A cross between ballet and chess," one character explains, to which another adds, "Throw in the Battle of Waterloo, and you've got something."

Irina knows Ramsey because he is the ex-husband of a children's book writer with whom she has collaborated. Lawrence is a huge snooker fan and is thrilled to have a connection to Ramsey. Every year on July 6, they celebrate Ramsey's birthday with him, until that fateful year when Lawrence is out of town and Irina and Ramsey are alone -- hence the title of Shriver's book.

Irina has to make her choice at the end of the first chapter, on Ramsey's 47th birthday. The rest of the book is actually two novels told in alternate chapters: In one version, Irina gives in to her desire to kiss the snooker star. In the other, she resists. In either case, there are changes great and small in her once-orderly world.

It's a complicated premise, and it took me time to grow comfortable with it. I found myself spinning the pages back and forth to recall precisely what was occurring in Irina's life in the alternate universes. Moreover, Shriver offers us Irina's world in precise, almost microscopic detail. We know a lot about how much popcorn she and Lawrence consume, and the spices with which she seasons it. The result is a book -- well, two books -- that occasionally feel a bit bloated.

On the other hand, when the device works, it is fascinating to watch how Irina's life is changed by a single kiss. Or, conversely, how it is transformed by choosing to abstain from that kiss. In one world, Irina will leave Lawrence for Ramsey, which sets off a litany of seismic changes. In the other, she will remain with Lawrence -- which results in a transformation of quite another sort.

Shriver has offered Irina two men who could not be more different. Lawrence is educated and erudite and even-tempered. He is lik able, but a little cold -- especially in bed. Irina and Lawrence never kiss, and they make love robotically. Ramsey, on the other hand, is an intelligent but uneducated snooker player: He is wealthy, mercurial, and a lover who happens to make Irina swoon. On the same airplane in the parallel universes, when Irina remains with Lawrence , the pair will watch another couple making love under blankets high above the Atlantic; when she chooses Ramsey, it is she and her snooker lover under those covers.

Ramsey is clearly the more handsome and the more charismatic of the pair, but a life with him will not be without problems. He travels often, his life revolves around snooker, and he is jealous. Her career may suffer.

Which is the real Irina? The hardworking illustrator ? Or the pampered, hard-drinking snooker floozy?

Moreover, Irina has trouble committing completely to her choice in either case, with the result that she makes her life needlessly hard. Why, for instance, would you invite your ex-lover to a literary gala when you know your current lover detests him -- and why would you wait until he shows up in the ballroom to drop the bombshell that he is coming?

Meanwhile, the question always lingers: Which was the better choice? A life of stability and pleasant company? Or one of ardent sex and sudden storms with a handsome London icon?

Some readers may find Shriver's answer in the end to be coy and a little careful. But they will also find her to be a writer with heart and a sly sense of humor. And so while I was occasionally frustrated with Irina or I felt I was learning more about snooker than I wanted to know, there were other moments when I found myself riveted by "The Post-Birthday World."

Chris Bohjalian is the author of 10 novels, including "Midwives" and "The Double Bind," which has just been published.