Charlotte is a former bank employee who currently lives in isolation on the second floor of her apartment building. She rarely leaves her home due to safety concerns regarding a stalker who has severely restricted her autonomy. Trained in self-defense and equipped with protective gear, she maintains a hypervigilant lifestyle to manage her fear. The sudden disappearance of her building's stairs initially brings her a sense of relief and safety from the outside world.

Seth is an arborist recovering from an ankle injury and a recent divorce. He uses a walking boot and maintains a deep passion for trees, which he often discusses when nervous. Volunteering at a local retirement home teaching bonsai classes, he values community and connection. Being stranded on his apartment landing prompts him to reach out to his reclusive neighbor.

Izzy is a private investigator and Charlotte's fiercely protective best friend. She teaches self-defense classes and provides practical security advice to help Charlotte manage her restricted lifestyle. While highly competent in her professional life, she struggles with romantic relationships and admits to a habit of pursuing emotionally unavailable men.

George is a former bank client who developed an intense obsession with Charlotte after she assisted him at work. Following a ban from the bank due to his disturbing behavior, he escalated his actions, resulting in a brief jail sentence and a restraining order. His unpredictable whereabouts dictate Charlotte's extreme security measures.

Gabe is Seth's close friend who provides practical support and advice. He helps set up a bucket-and-pulley system to deliver supplies to the stranded second-floor residents. He encourages Seth to avoid oversharing about his botanical interests and pushes his friend to embrace the opportunity to socialize with his neighbor.

John is the property manager of the apartment building where Seth and Charlotte reside. He takes responsibility for the construction mistake that removed the wrong staircase. He coordinates accommodations for the stranded tenants, setting up a pulley system and bringing them necessary supplies over the holiday weekend.

Cecilia is Seth's ex-wife. She recently ended their marriage by cheating on him with a distant relative. Her actions leave Seth navigating a painful emotional recovery as he tries to rebuild his life.