DOUBLE WHAMMY By Carl Hiaasen Putnam. 320 pp. $16.95

This is a murder sizzler that's got everything -- outlandish characters, withering wisecracks, gruesome deaths, a hilarious sendup of TV evangelism and, not least, an introduction to the frenetic world of fishing for largemouth bass, America's fastest growing outdoor sport and one in which professionals compete for very big bucks indeed.

"Double Whammy's" hero is R.J. Decker, once a Miami newspaper photographer, now a burned-out case and part-time private investigator. His new client is the rich and arrogant businessman Dennis Gault, a bass-fishing fanatic who offers him $50,000 to get pictures of Dickie Lockhart, a rival he hates, slipping ringers into his catch at a bass-fishing tournament. Decker accepts what will become a dangerous assignment, even though he knows nothing about bass fishing and just listening to the despicable Gault gives him the sensation of being "stuck in an elevator with a Jehovah's Witness."

The book comes to a reasonably happy ending after three murders, two justifiable homicides, a violent death during a bass tournament and the kidnaping of Decker's lovely ex-wife Catherine.

The first murder victim is the bass fisherman Bobby Clinch, who, Decker will learn, was Gault's first choice to investigate the bass scam; No. 2 is a dim reporter who dies because for once he does some digging; No. 3 is Dickie Lockhart himself, the fisher king and supposed chronic cheater.

Decker gets help from a mysterious hermit named Skink who is variously described as a maniac, a giant fruitcake and a man with only "one oar in the water." Also helping are Skink's friend from the past, Jim Tile, a black state trooper who outwits and outmuscles the racist bullies of remote Harney County, and Sgt. Al Garcia, a Cuban American Miami cop who hates trailer parks and believes they "were the reason God invented tornadoes."

The forces of evil include Gault, who resents being treated like a "peeling leper" by blue-collar bass-blasters because he drives a Rolls-Royce instead of a truck, and the Rev. Charles Weeb, the scheming, greedy, foul-mouthed, sexually voracious evangelist who owns the Outdoor Christian Network, a conglomerate including cable TV, investment banking and land development. Then there are Gault's sexpot sister Lanie and Tom Curl, a tigerish hit man.

What makes the book great fun is author Carl Hiaasen's Menckenizing of everything corrupt, phony and swinish under the Florida sun. So I'll mute my complaints about elusive motivation, gratuitously ghastly descriptions and the misuse of the word "disinterested."

Hiaasen, a prize-winning investigative reporter for The Miami Herald, is now a columnist there. He collaborated with William D. Montalbano on three novels before his first solo success, the zany "Tourist Season," in 1986. "Double Whammy" places Hiaasen up there with Ross Thomas and Donald Westlake as a wildly imaginative caper writer.

Here, for instance, is the unusual Harney County morgue: "While the Burger King sign had been removed (and sold to a college fraternity house), the counters, booths, and drive-up window remained exactly as they had been in the days of the Whopper ... it was the only place in Harney with a walk-in freezer."

Skink is by far the weirdest character, with his appetite for road kills (including flattened armadillo), his attire (sunglasses, long, braided ponytail, flowered shower cap, orange rain suit, Marine-style boots) and his intimidating greeting to strangers while hefting a rifle.

Almost as eccentric is the Rev. Mr. Weeb, employer of Dickie Lockhart on the immensely popular "Fish Fever" show. But Dickie's ratings had slipped just when Weeb needed him to promote Lunker Lakes, the "Christian community" of 29,000 town homes ($150,000 each) he had built on the edge of the Everglades after bribing the appropriate officials.

On the eve of the Dickie Lockhart Memorial Bass Blasters Classic, designed to goose lagging sales at Lunker Lakes, Weeb badly needs a miracle that will get the donations pouring in. The bank that lent him 24 million neatly laundered dollars -- First Standard Eurobank of Ohio -- has gone belly up and now it's discovered that Lunker Lakes has been built on the site of a landfill that contains every toxic chemical known to science.

The evangelist plans to stage a fake healing on cable TV. Gault plans to win the tournament with the biggest scam of all. Both are in for big surprises.

I went for "Double Whammy" hook, line and sinker, and I think you will too.

The reviewer, retired book editor of the Cleveland Plain Dealer, lives on Maryland's Eastern Shore.