The following version of the book was used to create this study guide: Frankel, Laurie. One Two Three. Henry Holt & Company, New York, NY, 2021. Kindle AZW file.

One Two Three, a novel by Laurie Frankel, is the story of triplet sisters who live in the small town of Bourne. Mab Mitchell was the first born of the triplets. Her sister Monday was born second, and Mirabel was third. Nora Mitchell is the mother of the triplets. As is the case sometimes with multiples, the sisters have developed their own shorthand to communicate, referring to each other by number rather than name. Mirabel has a neurological disorder. Confined to a wheelchair, she is unable to feed or dress herself or tend to other daily needs. Since Mirabel is unable to speak, she uses an app on a tablet to communicate. She is able to communicate some messages to her sisters and mother without the tablet. Although Mirabel is incredibly intelligent, she is in a limited class at school, meaning she oversees much of her own education online. Monday is high-functioning autistic. She does not like to be touched. She prefers only yellow or green clothing and food, and she takes most situations literally. She often misunderstands facial expressions and depends on Mab or Mirabel to help her understand jokes. Mab has no deficits, which creates challenges of its own. Because she is classed as Track A in school, she is expected to work as a tutor for students who are struggling. She has come to believe that she must give of her time and herself because she was not born with any of those deficits common in Bourne. She has hope for a future outside Bourne.

Bourne was a typical small town two decades earlier when the Templeton family opened the Belsum Chemical Plant. The plant brought the promise of good jobs and growth for the town, and most of the residents welcomed the opportunity. However, the river soon turned green, and people and animals developed health problems. By the time the plant was forced to close, many of the residents had died, including Nora's husband. Many others had terrible health issues, and children were born with all sorts of deficits. Nora led the charge with a class-action lawsuit that eventually died for lack of interest and evidence.

As the 16-year-old triplets begin another year of school, the residents discover that a new family has moved to town – Nathan Templeton with his wife Apple and their son River. They are paving the way for the reopening of the Belsum plant, this time under a new name and with Nathan pledging that the chemical is safe. Some are willing to allow the plant to reopen because they are desperate for jobs and benefits. At least, this plant offers more hope than they have had recently. Others are skeptical that the chemical is any safer than it was in the past. Mab, Monday, and Mirabel find proof that the city actually owns the dam that provides water to the plant and that Belsum cannot open without that water supply. Nora plans to file an injunction, but that fails. The triplets discover that the chemical analysis has again been manipulated, meaning the citizens are setting themselves up to be poisoned again. The sisters take matters into their own hands, stealing a backhoe and destroying the dam, setting Bourne on a path to recovery. Over the next few years, Mab goes to college. Monday becomes the town's librarian, and Mirabel begins a newspaper. Nora agrees to a settlement of the lawsuit and finds love. The residents of Bourne begin making some progress toward revitalization.