Just as Vidal’s Myron Breckinridge, fond husband and loyal Republican, is periodically taken over by his transsexual alter ego, Myra, so the author of such historical novels as “Burr” periodically gives way to the slash-and-burn satirist. (The last outbreak was the 1983 “Duluth,” a poststructuralist sendup of ‘Dallas.’) “Live from Golgotha” reassures us that Vidal still hasn’t gone respectable: Christians and Jews, p.c. gays and uptight straights will all find plenty to offend them. The premise is bracingly blasphemous: NBC-TV goes back in time to film the Crucifixion, and chooses Timothy to anchor the broadcast. Meanwhile, a computer virus is retroactively altering the Gospels. Only Timothy’s writings will be immune, and he must tell the true story of Jesus in order to save Christianity as Judgment Day nears.

After the brain-straining twists and turns customary in time-travel as-one character’s nemesis is his younger self-we finally learn who “the Hacker” is, why he’s out to destroy Christianity and the truth about Jesus’ weight problem (“Look, there’s been talk of splitting you up into three parts,” says prototrinitarian Paul). We also learn we can’t what we’ve just read. Such anachronisms as ancient Romans playing bridge Paul’s vision on the “Jerusalem-Damascus freeway” suggest Timothy isn’t immune at all; his narrative has been altered by contact with people from the future. “Every time one of them pays me a call,” he notes, “I begin to write odd things. . .” Timothy’s slangy irreverence-“John Mark split, leaving an opening not only in Saint’s office staff but sack, too”-may be another symptom of viral contamination; after all, even the book’s title turns out to be inaccurate. Or it may just be Vidal wising off.

“Live from Golgotha” ingeniously repackages Vidal’s familiar themes. He’s an unbeliever who’s obsessed with the apocalypse and messianic figures, from Myra (who seeks to realign the world sexually) and Kalki (the Vietnam vet and avatar of Vishnu who seeks to destroy it) to Burr and Lincoln. He’s a skeptic about historical truth who’s our best historical novelist. And, as he boasts in “Screening History,” he’s always been “a royal pain in the ass.” A good guy for earnest Cousin Al to avoid, especially with voters watching. But those weary of election-year pieties will find him entertaining company with his systematic subversion of every known value except, of course, intelligence, wit and imagination.