Under the pen name Gourmand, Handa Hikosuke writes scathing online restaurant reviews, targeting a food industry he believes is corrupted by money and power. Hikosuke was once the owner-chef of a small creative cuisine restaurant, but a famous critic named Asoyama Ryoko penned a fabricated review that destroyed his business. Now 33, he operates as a masked critic, dressed in a three-piece suit with a bowtie and fake mustache, speaking with deliberately odd Japanese phrases. His twin goals are to reform gourmet criticism into something fair and honest, and to train his palate so he can eventually reopen his own restaurant.

Asoyama is a beautiful but unscrupulous critic who takes bribes to write glowing articles or to ruin rival establishments. She remains Hikosuke's nemesis, though later encounters reveal her own troubled past. Hikosuke is soon joined by an eccentric fan, Kogane-ya Hiromi, a 27-year-old space designer who has read every one of his blog posts and mimics his strange speech. She begins to accompany him on his dining investigations, often helping to uncover the truth behind the food.

The story follows Hikosuke and Hiromi as they visit a variety of eateries: a sushi joint that serves mediocre fish but charges premium prices, a steakhouse using inferior cuts, a centuries-old eel shop resting on its reputation, and many more. Hikosuke's critiques are always brutally honest, neither flattering the restaurant nor deferring to popular opinion. He challenges not only the food but also the behavior of pretentious customers and the manipulations of corrupt critics.

Over the course of the eight-volume series, the narrative explores deeper questions about the purpose of criticism. Hikosuke's rigid mission to “correct wrongs” gradually softens as he meets chefs who pour their lives into their cooking. A key arc involves a cooking showdown between Hikosuke and Hiromi, where she tests his commitment to the role of critic versus that of chef. Meanwhile, Asoyama's disciple and other industry figures confront Hikosuke, forcing him to reconsider what honest criticism truly means. In the final volume, Hikosuke resolves to update his approach, focusing on supporting restaurants rather than simply tearing them down, just as a new threat looms over his journey. The manga concludes with Gourmand continuing forward, love for food guiding his every word.