Taking both paths at the fork in the road

By Lionel Shriver

HarperCollins. 517 pp. $25.95

nolead ends 'What might have been" haunts lovers, bedevils military strategists, distracts well-behaved dogs, and inevitably pesters everyone. Thankfully, the urgencies of the day relieve most of us of ongoing, painful concentration on alternative scenarios. Novelists, though, come with imaginations that won't let go, not to mention open afternoons and empty screens to fill.

For American novelist Lionel Shriver, a native North Carolinian who graduated from Columbia University and then chose to spend much of her professional life overseas in Belfast and London, a particularly bright scenario has been playing out in the last two years.

After decades of producing six strong novels that drew respectful reviews but not the prizes or publicity campaigns that break a writer out of the generational pack, her seventh book, We Need To Talk About Kevin, probing the distraught mother of a Columbinelike teenage killer, won the 2005 Orange Prize for Fiction, one of Britain's biggest.

Since then, a rosier story continues to unspool. Shriver writes regularly for publications such as the Financial Times, and The Post-Birthday World - her ingenious new novel about a woman torn between two men - is being welcomed as the latest from a recognized mid-career master.

The plot, or plots, devolve in part from Shriver's own life, in which she lived for a couple for years with the international policy analyst Jonathan Stevenson.

In The Post-Birthday World, Irina McGovern, a 42-year-old American children's-book illustrator who shares a place in London with think-tank type Lawrence Trainer, has fallen into the annual ritual of celebrating the July birthday of Ramsey Acton, a star at snooker (a form of British pool). Acton, a pal of Lawrence's, is married to Jude Hartford, an author with whom Irina has worked.

As the tale begins in the late 1990s, the annual ceremony looms, but with a difference. Ramsey has split with Jude. Lawrence is off at a conference. Irina must decide whether to dine with Ramsey alone, on his 47th birthday, to keep the tradition afloat. After a flirtatious phone call, she decides to do it, soon faces the urge to "fasten her mouth on the wrong man," and that's where Shriver launches the book's delightful structural experiment.

In alternating chapters, Shriver tells two stories: what happens if Irina chooses Ramsey over Lawrence, with whom she's spent nearly a decade, and what happens if she stays with Lawrence. If Shriver could work out such persuasive scenarios for everyone, she'd be bigger than Microsoft and Google. As it is, she has produced a novel that's equal parts entertainment and psychological massage.

Life with Ramsey on the snooker trail turns out to be exciting (as in sex that finally sizzles), embarrassing (Ramsey can't be counted on to behave well, like reliable Lawrence), and daunting. Ramsey's a bit of a celeb in his world, a somewhat vulgar one to boot, even if one character laughably describes his sport as "a cross between ballet and chess."

Life with Lawrence as a well-educated couple feels like an endless casual seminar in which Lawrence ruminates about Northern Ireland and Irina steers her successful publishing career. It moves forward as such safe, friendly alliances tend to, with tight-mouthed kisses, without fireworks or fire. Security and companionship trump all. What's predictable is that everything will be predictable.

Sturm and Drang or wine and cheese? Been there, but not sure if you should have done that?

A bracing question arises. Are we experiencing the same Irina in both narratives? Not if she and we are the sum of our actions. Yes, without doubt, if we're the uncertain upshot of our sensibilities, which can tip us in different directions. Convincing us that Irina is the same personality in both stories counts as one of Shriver's foremost feats here. While The Post-Birthday World may not replace Sartre's Nausea or Beauvoir's She Came to Stay on world-lit reading lists, it stands as a wholly realized existentialist novel.

Yet, don't think that The Post-Birthday World is a write-by-the-numbers implementation of a calculated novelistic scheme. Shriver's signature mix of introspective questioning and droll articulation of familiar human moments results in merriment and insight along the way. One pleasing device is describing the same event differently in each narrative, such as a visit to Irina's mother. In a particularly puckish juxtaposition - make that just "position" - Irina in the "Stay With Lawrence" tale watches another couple making love under blankets during an airline flight. In the "Rock With Ramsey" story, it's Irina getting it on under the covers. (Call it the Two-Story-High Club.)

The moral lessons suggested by The Post-Birthday World won't revolutionize romance or human choice. Shriver hangs one truism on the front door of the book as its epigraph: "Nobody's Perfect," with the tart attribution, "Known Fact." Another might be, "You Can't Win," given that whatever choice Irina makes brings a rebuke or sardonic eye-rolling from someone in her life.

We all need to talk about commonsense truths and lost opportunities. What Shriver adds is the arresting thought that imaginatively sketching out, at 500 pages, the consequences of one life choice or another might bring clarity to our hopes, dreams and decisions.

Then again, it might not.