Dave Hall, a 53-year-old game warden with the U.S. Fish and Wildlife Service, in no way fits the stereotype of the fellow who collars your cousin for fishing without a license. A man obsessed, he works around the clock as an undercover cop chasing wildlife poachers from Louisiana to Alaska. He and his kind are like characters from the last century. As author Marc Reisner points out, “Backup DEA agents hide in nearby buildings or vans, backup wildlife agents actually hide behind trees, or in trees.” But their foes - Cajun river rats, Alaska motorcycle gangs, Long Island gangsters - are decidedly modern, and altogether vicious. They are not putting food on the table. They are slaughtering for big bucks.

In this exciting, disturbing book, Reisner, author of the environmental cult classic “Cadillac Desert,” points out that there is a lot more to poaching than just money. There are, after all, a lot of easier ways to make an illegal dollar than by hunting alligators or cutting the tusks off walruses in the Bering Sea. Blood lust and a deep-seated loathing for authority have a lot to do with it, too. This is, Reisner reminds us, the country that wiped out the buffalo pretty much for the hell of it.

Reisner ladles on the statistics, some of them tragic (25 million buffalo wiped off the Great Plains in 50 years), some hopeful (alligators in Louisiana, where they were slaughtered almost to extinction 30 years ago, now number around half a million, thanks to state and federal protection). But what lifts “Game Wars” above the level of just another politically correct environmental book is the complicated character of Dave Hall. Fiction is full of detectives who identify with their foes, but Hall is the real thing. He spends weeks at a time pretending to be the sort of person he despises, ingratiating himself with the enemy, making what look like lasting friendships that inevitably end in betrayal.

He insists his Jekyll/Hyde routine is a necessary part of his job: “You show me a game warden who’s so correct he won’t hunt and fish anymore, and I’ll show you he ain’t worth a damn at the job. Those are the same kind who’re ineffective as undercover wardens. They hate the outlaws so much they can’t even associate with them. You can’t be an undercover agent if you aren’t willing to associate with a lot of riffraff.”

Reisner thinks it’s more complicated than that. He points to the fact that Hall hunts not merely out of obligation but because he enjoys it. In other words, this game warden really is like a fox set to guard the henhouse. It’s just a matter of how many chickens you take. While Hall believes that people can use nature without butchering it, his ability to think like a poacher depends in no small measure on recognizing the poacher’s rapacity in himself. Reisner’s success at forcing the same realization on his readers makes “Game Wars” one of the most disquieting books ever written about environmentalism.