Futurist wunderkind Womack (Random Acts of Senseless Violence) concludes his heralded Ambient series with this intriguing, clever novel set in an alternate, semihistorical 1968. Some details are familiar: the Velvet Underground is playing small New York City clubs; hallucinogenic drugs are popular and potent. But a Republican, Henry Cabot Lodge, has been president for years, and all African-Americans in the country have been deported, forcing those with any black heritage to keep it disguised. Drifting through this alternate universe is Walter Bullitt, a drug experimenter who talks like a beatnik crossed with John Shaft: ""I cooled on my slab till roostertime"" translates roughly as ""I slept until dawn."" Bullitt takes on occasional blackbag operations for the government dosing unsuspecting citizens with drugs in order to observe the results but has second thoughts when he's asked to prevent the upstart Robert Kennedy from running in the presidential election. As he's mulling over the Kennedy job, things begin to get weird: he sees ghosts, he's invited to join a cult, and a bizarre pair of women hijack him for unknown purposes. In short order, Bullitt finds himself at the center of a time/space crisis that threatens to destroy at least two different worlds. Although his hero's vernacular may annoy some readers, Womack has crafted a fast-moving, hipper-than-hip science fiction novel meshing the exuberant wordplay of Anthony Burgess with the high-concept what-if history Philip Dick made famous with The Man in the High Castle. (Mar.) Forecast: This final, top-notch Ambient installment has the potential to generate considerable crossover appeal while satisfying old fans. Those in the know will correct anyone who tries to call this cyberpunk lit no ""cyber"" is involved but readers of William Gibson should gravitate toward Womack.