Seventeen-year-old Duncan struggles with severe guilt after witnessing a young woman's drowning the previous summer. Living in a dilapidated neighborhood known as the Jungle, he views the world with profound pessimism and expects to fail. When he discovers a disturbed individual's journal at his transit station job, he seizes the opportunity to track the author down, viewing this pursuit as a chance to finally do something heroic.

Known only by a self-assigned nickname based on his hard-to-kill nature, Roach is the mysterious author of a lost journal found at the transit station. The notebook reveals a deeply disturbed individual with an escalating history of animal cruelty and setting fires. He meticulously documents the physical characteristics and daily schedules of young women on the subway.

Vinny is a clever teenager who acts as the intellectual anchor of Duncan's friend group. Born with a withered arm and missing fingers, he frequently invents wild stories to explain his physical differences. He proves highly capable at organizing information, mapping out transit routes and studying true crime books to narrow down their suspect's location.

Wayne is a street-smart teenager with a history of petty theft, including a failed attempt to steal toilets alongside Duncan. Though he currently works legally and expresses a desire to avoid prison, he struggles to resist the lure of illegal activities. He maintains a fierce loyalty to his friends despite being initially excluded from their investigation.

Jacob is a quiet man who manages the Toronto Transit Commission's Lost and Found, an underground office he refers to as the morgue. Dealing with the tragedy of his comatose wife, he actively seeks out predictable, isolated environments to avoid further emotional turbulence. He offers unsolicited but practical advice about accepting the bleak nature of the world.

Duncan's mother is a dedicated student taking community college courses while working part-time. She finds genuine joy in learning and frequently watches classic films in her downtime. She constantly worries about the well-being of her family, and her quiet disappointment serves as the strongest deterrent against bad behavior in her son's life.

Working exhausting night shifts repairing an assembly line that makes catalogs, Duncan's father is a worn-down man whose exposure to industrial glue has deadened his physical senses. He harbors lingering regrets about missing his chance to be heroic, often sharing a story about a remorseful Secret Service agent. He frequently urges his son to use the dreary summer job as motivation to escape their neighborhood's poverty.

Maya is a young woman who drowned at Kayuga Beach the previous summer. Though she is already deceased when the story begins, her presence looms large over the narrative. She embodies the moment of perceived failure that drives the protagonist's desperate need to intervene in another tragedy.

Kim is a compassionate teenager who volunteers her time at Gatherup, a local center for homeless children. She values living fully and refuses to be dragged into a pessimistic mindset, which ultimately led to the dissolution of her year-long romance with the protagonist. She maintains firm boundaries but still cares deeply about the well-being of those around her.