It takes place seven years after the original game, in 2019. The protagonist of One Night: Full Circle is Tom Hawkin, who travels to the town of Stillwater to search for a missing relative, only to find it abandoned and infested with monsters and shadow people. In Stillwater, he meets Colt, the protagonist of One Night who has also been drawn to the town, and the two team up to discover what has happened to the town and how it is connected to the events of the previous games.
In the course of exploring the town, Tom and Colt learn that following their defeat at the end of the second game, the shadow people left "The Beyond" behind to find other ways to regain their lost power. Seeking to create an influx of negative energy to reinvigorate them, they placed John Faraday (one of the protagonists of One Night 2) under their control and used him to blackmail a government researcher, leading to the events of One Night. As they were foiled by Colt, they were once again left powerless, and the catastrophe that has befallen Stillwater is yet another attempt to rupture the fabric of reality and gather more power. Full Circle covers the shadow people's final attempt to control humanity and, depending on decisions made by the player during the game, they either succeed or fail in one of two different endings.