If a national magazine were to devote a cover story to boxing today, veteran journalist Joe Layden writes in “The Last Great Fight” (St. Martin’s, 320 pages, $24.95), it would probably run under the headline, “Whatever Happened to Boxing?” If you want to know what happened to the sport that produced such American legends as John L. Sullivan, Jack Dempsey, Joe Louis, Rocky Marciano, and Muhammad Ali, Mr. Layden’s exhilarating and hard-hitting account of the 1990 heavyweight championship fight between Mike Tyson and Buster Douglas and its aftermath will tell you, and the picture is about as pretty as Sylvester Stallone’s face at the final bell in a “Rocky” movie.

In Tokyo on February 11, 1990, to the mute astonishment of Japanese boxing fans, an unheralded challenger from Ohio named James “Buster” Douglas scored perhaps the biggest upset in heavyweight boxing history when he knocked out the seemingly invincible champion Mike Tyson in the 10th round. Mr. Douglas was a 42-to-1 underdog — if you could find anyone who would take the bet. To put that in perspective, consider that the famed Cinderella Man, James Braddock, was only a 10-to-1 underdog when he beat Max Baer for the title in 1935.

The upset should have made Mr. Douglas a national hero and given boxing a much needed boost. Instead, it led to the swift unraveling of the careers of both Mr. Douglas and Tyson, both of whom were never the same again. Boxing began, Mr. Layden writes in prose as crisp as a Sugar Ray Robinson jab, “a long and precipitous slide toward the margins of mainstream sport.”

Tyson is credited by Mr. Layden — perhaps a tad too generously, as at least one prominent boxing commentator regarded him as “a cancer on boxing” — with briefly resurrecting the fight game. He was undeniably the biggest draw in the heavyweight division since Mr. Ali at his peak. It was Tyson’s “menace and bloodlust that brought people to the arena, that compelled otherwise frugal and sensible consumers to spring for a Home Box Office subscription.” No heavyweight since Louis demolished his Bum of the Month Club in the late 1930s seemed so devastating.

Mr. Douglas, the son of a veteran fighter, was “a thoughtful, introspective boy” who “loved boxing, which is not to say that he enjoyed fighting,” Mr. Layden writes. For just one time in his life, Mr. Douglas was able to focus his energy and attention on training, and he beat Tyson so decisively that many thought he would rule the heavyweight ranks for years. For at least a year, Mr. Douglas was the highest paid athlete in the world, but in his first title defense, against Evander Holyfield, he was so listless and overweight that many thought his defeat by a fourth-round knockout was a disgrace. Tyson, meanwhile, demoralized by the loss of his crown, descended further into a pattern of violence and self-indulgence, leading to a rape conviction in 1992 that kept him in prisons for most of his prime years. The much-anticipated Douglas-Tyson rematch never happened.

Mr. Layden doesn’t belabor the obvious — there’s no need to. The villain in the story is promoter Don King, who, with Tyson as his meal ticket, tried to have the result of the 1990 fight overthrown on a technicality. Failing that, King actually moved to Mr. Douglas’s hometown of Columbus, Ohio, and coaxed Buster’s father, as well as the director of the National Association for the Advancement of Colored People, Benjamin Hooks, into convincing Buster to leave his white manager and throw his fortunes in with King. “I was harassed every day I was heavyweight champion of the world,” Mr. Douglas recalled for Mr. Layden. “By the time the Holyfield fight came around, it was total chaos in our camp.”

Later, when Mr. Douglas lost his title, King hooked up again with Tyson, who eventually sued King for $100 million for stealing from his purses; Tyson was awarded $14 million but spent most of it settling numerous suits ranging from assault to past-due trainer’s fees. Mr. Douglas, meanwhile, made one failed attempt at a comeback and was then diagnosed with diabetes. As Tyson’s former publicist Mike Marley crassly put it, his man went to prison while the “other guy becomes a happy fat man with a terrible illness. I don’t think you can find a better soap opera than that.” If Mr. Douglas wasn’t exactly happy, he at least walked away from boxing contented, having invested his money wisely, something as rare in the sport as is a white heavyweight champion.

There were, of course, many reasons for boxing’s decline besides Tyson’s and Mr. Douglas’s fortunes, beginning with the lack of regulation that allows predators such as King to operate. There is the drying up of the talent pool; as HBO boxing analyst Larry Merchant put it, there are hundreds of potential heavyweights out there — “[a]nd they’re all playing linebacker” or engaging in other safer, more lucrative sports. Most of the potential audience for boxing, outside of Hispanic communities, has become more jaded, defecting for the cheap thrills of wrestling and mixed martial arts.

But whatever the reason, it’s likely that boxing, if not dead, is unlikely to ever produce a fight of such widespread significance as the Tyson-Douglas match. Boxing fans will want to add “The Last Great Fight” to the vast collection of great books on the Sweet Science, from Ernest Hemingway to A.J. Liebling to Norman Mailer. Just file it at the end of the shelf; it’s the last book you’ll ever need.

Mr. Barra writes about sports for the Wall Street Journal and The New York Sun, and about books for The New York Sun and the Washington Post.