Nora is a thirty-five-year-old woman living a lonely, monotonous life in Bedford, England. After a series of rapid setbacks including the death of her cat and losing her job at the local music store, she reaches a breaking point and attempts suicide. Though she possesses a wide variety of talents—she was once a competitive swimmer, a philosophy student, and a rock singer—she is consumed by regret over abandoned dreams and perceived failures.

Mrs. Elm is the supportive school librarian from Nora's youth who offered her guidance and stability when her father died. Within the mysterious Midnight Library, she appears as Nora's guide, maintaining her familiar, prim appearance. She instructs Nora on how the magical books operate, explaining the rules of the space with a mix of strictness and compassion.

Joe is Nora's estranged brother who struggles with depression and keeping a steady job. He previously played guitar in a rock band, The Labyrinths, alongside Nora and his best friend, Ravi. He harbors resentment toward Nora for abandoning the band just as they were on the verge of success, creating a painful rift between the siblings.

Ash is a local doctor in Bedford who occasionally visits the music store where Nora works. He previously asked Nora out for coffee, though she declined at the time because of her relationship with Dan. He demonstrates quiet compassion during difficult moments in Nora's life, representing the value of small, steady acts of kindness.

Dan is Nora's former romantic partner. The couple planned to marry and open a countryside pub together, but Nora canceled the wedding just two days before the ceremony. He strongly disliked Nora's music career, preferring that she focus on his dreams rather than her own aspirations.

Hugo is a confident, inquisitive French scientist who recognizes that Nora is behaving unusually during an expedition in Svalbard. He possesses unique knowledge about the quantum mechanics of moving between different lives. He actively enjoys sliding through different versions of his existence, approaching life with a thrill-seeking attitude.

Izzy is Nora's best friend. The two women originally planned to move to Australia together to observe whales and start a new chapter. Their relationship became strained when Nora backed out of the move to stay in Bedford, leaving Izzy to travel and build a life alone.

Ravi is Joe's best friend and the former drummer for The Labyrinths. Since the band dissolved, he cleans toilets to make ends meet while looking for low-paying music gigs in local pubs. He maintains a hostile, bitter attitude toward Nora, openly blaming her for ruining their chance at signing a record contract.

Voltaire, affectionately called Voltsy, is Nora's ginger tabby cat. He is an independent pet who brings Nora her only consistent companionship in her Bedford apartment. His sudden death acts as the final catalyst that pushes Nora to write a suicide note.

Neil is the owner of String Theory, the small music shop where Nora works. Rather than offering sympathy when Nora explains her cat has died, he critically analyzes her past decisions before abruptly firing her from her job.

Geoff is Nora and Joe's father. After a severe injury ended his own athletic aspirations, he placed immense pressure on Nora to become a professional swimmer. His profound disappointment when she quit created a permanent fracture in their relationship before his sudden death from a heart attack.

Dylan is a blond boy from Nora's school who grows up to be a gentle, quiet presence in Bedford. He loves dogs and appreciates the calm pace of his hometown, offering a sharp contrast to the high-pressure lives Nora sometimes envisions.