Joy Nash plays ghostwriter and apparent scarf enthusiast Plum Kettle in “Dietland.” (AMC)

“Dietland” (9 p.m. Mondays on AMC) is the story of Plum Kettle — not your typical TV lead character. In voiceover narration she reveals that Plum is her nickname — bestowed because she is “succulent and round, also known as fat.”

Aware that the word “fat” is charged, she adds. “I’m allowed to say it.”

The actor Joy Nash, who plays Plum with an air of melancholy, states that she herself is “fat” at 293 pounds and not at all self-conscious about it. But Plum is. When she walks down the street, men hurl fat insults at her. She is saving her money for a surgery so she can drop pounds and live “a big, sexy life.” She earns a living mainly by ghostwriting an advice column for a women’s magazine called Daisy Chain, whose readers pour out their hearts to the editor about body image, cutting themselves and more.

That editor is Kitty Montgomery, portrayed with gleeful hauteur by Julianna Margulies of “The Good Wife.” Kitty is the opposite of Plum in every way, so thin that a reader writes, “You’re so pretty, even though you look like a skinny waxed Dracula.”

Kitty appreciates Plum’s insightful writing but does not want to assign her enterprising articles. She just wants her readers to adhere to impossible standards of beauty. And she’s caught up in some kind of fishy business that involves a “teensy” security breach.

Now that’s a good amount of plot for one show. But “Dietland” doesn’t stop there. A vigilante group called Jennifer is killing men who have been hostile to women. And Plum is recruited to join a revolutionary group that believes diets are “the root of all evil.” Adding to the mix are fantasy scenes and animations — in one, a corpulent Plum struggles to climb a mountain of twinkling pink desserts, growing thin as she ascends.

The result is a series that struggles to find an identity but is still worth watching, both for Nash’s bravura performance and for the witty and timely dialogue — like when Plum’s obnoxiously giddy “Waist Watchers” counselor tells her, “It will be hard to say goodbye to fat behaviors — like eating.”