First things first: The mushroom you find poking out of the duff in the woods or the grass of a field is “the fruiting reproductive body of a fungus, much as the cherry is the reproductive fruit of a cherry tree.” Unlike the tree, however, the fungus, which “lives underground in the form of threadlike filaments,” is invisible. Similarly, when morels or chanterelles appear on the menu of your favorite restaurant, they are the “fruit” of an underground network of pickers, buyers, and savvy chefs.

In “The Mushroom Hunters,” Langdon Cook explores both of these shadowy worlds. Along the way, we hear about the ecology of the different species, the best way to cook them, and the thrill of the chase, whether it is taking place in a stand of old-growth forest, a shantytown of cedar scavengers, or in “a horrible motel [with] blood on the floor and the shower was dirty and the sheets smelled of … .”

It’s a world that Cook has to admit is as much like drug smuggling as anything else, but “legal, or mostly legal.” He tees up the book by plunging the reader into a game of cat and mouse in Mount Rainier National Park between a forager and the rangers. Cook ends up driving the getaway car. “This makes me an accomplice,” he says. The forager agrees.

“My obsession with mushrooms arrived like a sickness,” Cook admits with no sense of regret. “Mushrooms are colorful, beguiling, hideous and transformative.” And given the rich diversity of his fellow obsessive invalids, it’s no surprise that he finds them at least as fascinating. There is the group of highly competitive morel enthusiasts with whom he rides on a school bus to an undisclosed location for the annual Boyne City (Mich.) National Morel Hunting Contest. They come from all over the country.

Then there are the commercial gatherers, people who carry maps in their heads filled with individual trees that are best for their particular quarry. These men and women are on a mission with no time to waste if they are to beat the competition and gather the mushrooms when they are at the right stage to command the best price.

The pickers are followed by buyers just as knowledgeable about the ways of the woods, whose “buy stands” – “often no more than a tarp or wall tent strung up in a gas station parking lot” – appear “ephemerally like insect hatches” wherever the picking is taking place.

Not the least pleasure of “The Mushroom Hunters” is the author’s knack for vivid simile. Smaller tree stumps – found around the base of a 1,000-year-old stump – are gathered “in tight clusters, like children at the feet of a storyteller.” Cooking a mushroom for which he was acquiring a serious taste at home “was like attending an experimental theater class.”

Cook also has a rich fund of interesting, not to say quirky, information:

One member of the bolete family, long prized by mushroom eaters, was only recognized by science five years ago. “One would be hard-pressed to find a commonly eaten food in either the plant or animal kingdom that lacks a taxonomic name,” he comments.

Italians call the meaty porcini “poor man’s steak.” But Cook notes that “these days, with the prices spring porcini are fetching, a person of lesser means might be more apt to have marinated New York strip on the grill.”

Another time he mentions a condiment called argan oil, from Morocco, which is made from seeds that must first navigate a goat’s alimentary canal.

“The Mushroom Hunters” does a masterful job of combining a multitude of narrative threads. In celebrating a particular mushroom, each chapter is replete with vivid descriptions of the various communities involved, many of them originally from southeast Asia. There are mouth-watering descriptions of wild-food feasts. And there are the personalities of the three main characters, a picker, a buyer and a chef. It says something that Langdon Cook was able to win the confidence these basically secretive people. All these stories are served up with an attention to brands – Tommy Bahama, Marmot, Grand Cherokee Laredo – that would make Ian Fleming blush.

Reminiscing about an old picker’s camp in the woods, someone tells Cook “… what made that place so damn interesting – the people!” The same can be said for “The Mushroom Hunters.”

Thomas Urquhart is a former director of Maine Audubon and author of “For the Beauty of the Earth.”