By Chris Elliott

Miramax. 358 pp. $22.95

This may be the most facetious novel ever written about a serial killer: I count 57 jokes in just the first 10 pages. Chris Elliott, the author, is a gifted comic actor whose performance as a stalker in "There's Something About Mary" may account for his ear for the lighter side of psychopathic behavior. The many-sided Elliott is also a character in the novel and its narrator. The action is framed by his efforts to identify -- with the forensic 20/20 hindsight of a funnier Patricia Cornwell -- the man known to history as the Thwacker.

Most of the book, though, is set in Manhattan in 1882, during the Thwacker's reign of terror. Like the Ripper, his transatlantic counterpart, he murders prostitutes and mutilates their corpses. On his trail are Police Chief Caleb Spencer, pushy reporter and love-interest Liz Smith and Mayor Teddy Roosevelt, who breaks wind about once a page till midway through the novel, when his disappearance clears the air a little and adds another twist to the investigation. Toward the end, the author joins them back in 1882, after a turbulent ride in a time machine.

"The Shroud of the Thwacker," in short, is relentlessly silly. Some of the silliness is very entertaining: "He made his way up Broadway, where he paused to buy a cup of mayonnaise from a street vendor. In 1882 a man named Hellmann had just invented this oil-and-egg delight, but he wasn't yet sure how to market it. He started with street carts, selling it like ice cream. New Yorkers were so crazy about the new treat that they were more than content, at present, to eat it from a cup with a spoon."

Elliott's mayonnaise stands, kerosene-powered cell phones and proto-Internet (available only in penny arcades and offering only one Web page) are funny because they make light of our refusal to understand the past -- our insistence on finding its customs and technologies preposterous.

Elliott's way of finding a whole era laughable, however, works less well when focused on specific people, historic or fictitious. With its gaslights and cobblestones and stenches, Elliott's anachronistic cartoon version of the past is "realistic" enough for a genre novel, but even a tongue-in-cheek thriller will be hard-pressed to thrill for nearly 360 pages if its characters are cartoons, too. Roosevelt, especially, is such a caricature as to make the personages met by Mr. Peabody and Sherman on their time travels look positively subtle. (Elliott is obsessed with the Roosevelts: He also wrote, produced and starred in a spoof of "Give 'em Hell, Harry" called "FDR: A One-Man Show.")

It's hard to see, though, how fully fleshed-out characters could survive in Elliott's world, or Elliott's prose. At 5.7 gags per page, there isn't room for much else in this climate: Once the zaniness exceeds a certain density, it creates an atmosphere that nothing else can breathe. It also makes the reader wonder if this funny book would be funnier if it cracked fewer jokes, since the bad tend to drown out the good.

Many of Elliott's jokes concern bodily functions. Others are more highbrow, and some of the best mix the vulgar and refined to produce an enjoyable jolt, like truffled Spam or maybe more like channel-surfing between "South Park" and "Masterpiece Theatre": " 'Shh! This stool's still warm,' he said, gesturing to a pile of excrement. 'And this copy of Moby Dick's been left open in the middle of a chapter. He must have left in a hurry.' "

More often, the excrement comes to our attention in the second half of the joke. Elliott's favorite gag is the Bathetic Letdown, a laugh-getter patented by Alexander Pope ("Or stain her honor, or her new brocade") and later mass-produced by Woody Allen ("Not only is there no God, but try getting a plumber on weekends"). Elliott is clearly a big Allen fan, and may well see him as role model, since for the most part -- and with all due respect to Jimmy Stewart's poetry and John Travolta's fiction -- the only Hollywood actors to cross over to print with laudable results have been comedians like Allen and Steve Martin. "The Shroud of the Thwacker" crackles with Woodyisms, such as the blind orphan "kept on by the gang because his lack of vision had heightened his other senses -- specifically his senses of irony, outrage and cruelty to animals."

If Elliott's morbidly keen sense of humor has dulled some of the other sensibilities we hope for in a novelist, at least it's produced a morbidly amusing book.