Rowbottom traces all of this with a sure hand, drawing details from her mother’s unfinished memoir and shaping them so that they make sense in her own. Much of the writing is lush yet alert to specifics. An ailing Midge, her chest hollowed out by a mastectomy, “sat at the dinner table in her bathrobe, soft blue with pink rosebuds scattered over the fabric like the cherry blossoms that littered the front lawn each spring”; a terrified Mary, hiding from her dying mother behind a toolshed, watched “the red and blue ambulance lights bounce off the icy ground.”

Jell-O, meanwhile, gets the full semiotics treatment, as Rowbottom shows how it went from a modern, scientific foodstuff to a relic of soul-killing suburbia. As sharp as her insights often are, this is a book in which Everything Signifies. Even a digression about the catacombs in an Italian monastery includes some Jell-O symbolism. You occasionally want to tell Rowbottom to ease up: Sometimes a Jell-O mold is just a Jell-O mold.

The product history is mostly illuminating, though, as Rowbottom shows how the brand tried to keep up with the times. Women’s changing roles were a particular spur to innovation. A 1970s Jell-O cookbook pitched itself to independent women, with a recipe for a Green Goddess Salad Bowl (lime Jell-O, sour cream, anchovies — for starters) that gestured at health food, even if it didn’t quite deliver it.

The cookbook also included a chapter on “Salads for the Slim Life” — a reprise of the one constant refrain through the brand’s history. Aside from wartime and the Great Depression, when food was scarce, Jell-O has long touted itself as a diet food. In the 1920s, the company released a low-calorie version called D-Zerta (an unnerving name more suitable for a chemical weapon), and saw its fortunes buoyed by the dieting craze of the mid-’80s.

Rowbottom herself was born in the mid-’80s, and shows up about halfway through the book. An only child, she struggled with an eating disorder and, like her mother, a hand that would stiffen into a curved claw at stressful moments. When the two of them learned about the girls in Le Roy, they immediately became obsessed. These girls, living in a declining industrial town, were dealing with their own traumas; could their twitching have been what some neurologists said it was — a conversion disorder, the logical response to a culture that doesn’t help them process their emotions?

Emphasizing such cultural explanations is a bold move, one that goes directly against Susan Sontag’s old admonishments against illness as metaphor. Mary herself was wrongfully dismissed by doctors who insisted she was “hysterical,” when in truth her body was riddled by carcinoid tumors. But then Rowbottom’s book is too rich and too singular to reduce to a tidy argument.

At her own wedding she longed to embrace her dying mother even though she was also scared of her. “I found her unfamiliar, rouged like a corpse, her tumid ankles peeking out, inflated and purple,” Rowbottom writes. The sentence is both gorgeous and grotesque; she knows that lived experience is more unruly than the stories we tell to contain it.