Sarai Walker’s debut novel, Dietland (Houghton Mifflin Harcourt),  is, to paraphrase one reviewer, a feminist manifesto disguised as a beach read. The story concerns one Plum Kettle, a twenty-something woman who weighs 300 pounds and works in New York for a teen-girl-aimed magazine called Daisy Chain. To be more precise, Plum answers emails from readers to Daisy Chain‘s editor, Kitty Montgomery. This she does in the persona of Kitty. But there’s a disconnect. Kitty’s magazine deifies thinness and conventional beauty. Her cover girls are rail-thin and urgently appealing to the male gaze.

Plum herself is a serial dieter and alienated from her body. She has a closet full of clothes for a thin woman, dreaming of the day when she will fit into them—and fit into a culture obsessed with thinness. She lives in a future that will never come, and in the meantime spends her days in a coffee shop answering Kitty’s emails and her nights alone in Brooklyn apartment.

What changes Plum’s life, and lifts this novel to another level of social critique, is her encounter with Verena Baptist. Verena is the daughter of a woman who made a fortune on a weight-loss program called the Baptist Diet. She sees her mother’s program as fraudulent, and now uses the wealth gained through it to write books and otherwise debunk expectations that women should be as thin as the celebrities who model clothes, appear in movies and television shows, and adorn magazine covers.

What’s more, as the novel advances, it appears that Verena and her colleagues may have connections with a feminist terrorist group that calls itself Jennifer and, among other things, kidnaps accused rapists and drops them from an airplane. Plum wonders what she’s got herself into. I won’t say more and spoil the suspense of the novel.

Dietland features well-drawn characters and a compelling plot. And it’s often funny. But it’s also a savvy and penetrating critique of the way our culture sees (and fails to see) fat people. (On her website, Walker urges reviewers to use the word fat  and says it’s preferable to overweight  or obese. There and in her novel, she makes a move similar to gays who reclaim the originally derogative queer.) The book is a call to thought, and maybe to action.