West Mariners like to pay attention to food. Menus proudly display the names of local farms and purveyors that provide ingredients, and residents love to debate the merits of different diets. But there are limits to how much even a careful consumer can know. In a new book, “The Truffle Underground,” former Light reporter Ryan Jacobs explores the mysterious, crime-riddled underbelly of the truffle trade and what it really takes to get the prized mushroom from the forest to the table. “We as journalists—and West Mariners—go after guys like big ag and the Koch brothers: basically giant, industry food companies,” Mr. Jacobs said. “And I think those guys are bad, bad as can be. But I also think there’s a degree of scurrilous behavior to smaller companies and smaller producers, and people figure, ‘Oh, if it’s small and artisanal—which is what the truffle trade is—it must be of high quality and totally above board.’ But I don’t think that’s the case.” Truffles—especially the white and black winter varieties—are a treasured rarity, and as such bring in a pretty penny not only for the farmers who grow them, but for the thieves who seek them out. Truffles seem like the fruit of happenstance; they grow out of the root systems of oak trees and are dispersed not by the wind—as are most forms of fungus—but by the digestive system of animals. In the prized truffle farms of France and Italy, thieves come at night, their efforts nearly impossible to stop in the cover of darkness and densely wooded forests. Even when farmers are able to harvest the truffles themselves, the mushrooms are often stolen along their route to a restaurant kitchen. Over the course of writing and researching the book, Mr. Jacobs walked deep into the forests of France and narrow roadways of Italian villages; he spoke to unscrupulous mushroom dealers and farmers fervent about their precarious trade. He was frequently taken aback by the levels of deceit and brutality that seem woven into the industry. In an attempt to thwart thieves (or fellow truffle hunters), people often leave out poisoned meatballs for dogs; in one instance, a French farmer shot and killed an alleged truffle thief on his property. The violence associated with the industry surprised Mr. Jacobs, who had previously reported on international crime in the vein of diamond heists. “You don’t expect such a vaudevillian crime with food,” he said. It also taught him that people don’t really understand as much as they think they do about the food in front of them. “Beyond what’s in your food, there’s this whole unregulated submarket connected to whatever product you’re buying,” Mr. Jacobs said. “I’ve noticed, even at really nice restaurants, the menu sometimes will get the name of the farms they source from wrong, and it just makes you wonder.” Some truffle traders will try passing off Croatian or Slovenian truffles as white Italian truffles, the most prized of the species. Mr. Jacobs said that pulling off a similar scheme in West Marin might be difficult, given the small community. “You’d be hard pressed to dream up a con in West Marin,” he admitted, “but I certainly think there are areas in San Francisco where they might say they are sourcing something from West Marin and they’re actually getting it from Gilroy.” One of the book’s main messages, Mr. Jacobs said, “is just to ask as many questions as you can about what you’re consuming—and, even then, you might still not know everything.” “The Truffle Underground” will be published on June 4 by Penguin Randomhouse. The author will read from the book, and sign copies, at Green Apple Books in San Francisco on Tuesday, June 11, at 7:30 p.m.