By Lydia Millet

Soft Skull. 489 pp. $25

History as we know it came to an end on July 16, 1945. On that day, the first atomic bomb was detonated on a test site dubbed Trinity in Los Alamos, N.M. At the exact moment of the flash, three of the scientists responsible -- Leo Szilard, Robert Oppenheimer and Enrico Fermi -- were propelled forward in time to modern-day Santa Fe, where they must come to terms with the legacy of their creation. Or so runs the conceit of Lydia Millet's complex and affecting (if sometimes maddening) fifth novel, Oh Pure and Radiant Heart.

Taken in and cared for by a disaffected librarian named Ann and her skeptical husband, Ben, the three scientists soon realize that nothing but complete worldwide disarmament will prevent Armageddon. They swiftly land their first apostle -- a conveniently wealthy sensualist named Larry, who brings with him a motley assortment of disciples, including trippy Japanese club kids and ex-Deadheads. Larry is rich enough to bankroll the whole peace movement, and before Ann can say "Left Behind," two of the scientists have moved out of her house and into fancy new digs. Soon the growing entourage takes its show on the road, bound for a massive march on Washington. When their message gets co-opted by a cabal of radical Christians who believe Oppenheimer is the fulfilment of biblical prophecy, the stage is set for an apocalyptic conclusion.

Millet has staked her novelistic reputation on taking chances. She is the author of George Bush, Dark Prince of Love and the PEN/USA award-winning My Happy Life, about a naive young woman abandoned in a mental institution. Oh Pure and Radiant Heart may be her biggest gamble yet; it also promises to have the largest payoff because, while its premise seems absurd at first, its message is anything but. Here Rapture takes on many guises, and it is fitting that in a novel exploring the lives of those who set out to play God, Millet would playfully mirror the New Testament, giving us everyone from a John the Baptist walk-on named Eugene to a wannabe Mary Magdalene documentary filmmaker and a Judas among the camp followers.

For the most part, the religious undercurrents are apt. Oppenheimer, who sincerely believed he was serving humanity by ending World War II, was later crucified by the anti-communists for his political leanings and opposition to the hydrogen bomb. Millet's portrait of him is the most complex in the book, as he reluctantly accepts the mantle of doomed prophet almost as penance for what he has brought into the world.

But Millet devotes too many pages to the wearying multitude of followers, most of whom we get to know only as deeply as their salient satirical traits: Sheila the New Age babbler, Webster the contortionist, Adalbert the Belgian food activist.

Millet's humor is far better showcased in the understated irony of the atomic history she weaves through the narrative, such as this advice offered in an educational filmstrip: "The Atomic Energy Commission says the best defense against an atom bomb is to BE SOMEWHERE ELSE when it bursts." Or there's the chilling tidbit that the majority of workers who staffed Pantex (the endpoint for assembling most American nuclear weapons) were born-again Christians who believed they were doing God's work in speeding along the Rapture.

Yet for all its zaniness, this book is a serious indictment -- not so much of the pothead zealots and religious End-Timers (they, at least, have embraced their own idiosyncratic raptures) but of Ann, Millet's perpetually sleepy and dreaming protagonist. Describing her girlhood reluctance to leave her warm bed and set foot upon a cold floor, she tells her husband, "There was this static feeling right then, this feeling of being frozen . . . torn between doing something and doing nothing. . . . I didn't recognize it back then but now I see what it was. . . . It was how I was going to spend the rest of my life." If the Anns of the world remain paralyzed, Millet seems to argue, agents of darkness will make their decisions for them.

In his last speech, delivered to the crowd but directed at Ann, Oppenheimer poses the book's central issue: "The question is not, who is the enemy. . . . The right question is: What is it in me that delivers the world into the hands of the enemy?" Sixty years after Trinity, with our own government developing nuclear "bunker busters" and conducting subcritical underground tests, it is a question Millet believes we should all be asking. *

Sheri Holman is the author of "The Dress Lodger" and "The Mammoth Cheese," short-listed for the Orange Prize for Fiction.