The 11-episode series follows 12-year-old Griffin Campbell, whose family has just uprooted their lives to move to the small town of Sulphur Springs and take ownership of The Tremont, an abandoned hotel, in hopes of restoring it into the lively vacation destination it once was. As Griffin begins his first day at a new school, he learns the hotel he just moved into is rumored to be haunted by the ghost of a girl who disappeared decades ago. Along the way, Griffin befriends Harper, a bright-eyed, mystery-obsessed classmate. Together, they uncover a secret portal that allows them to travel back in time. In the past, they’ll attempt to uncover the key to solving this unsolved mystery, a mystery that affects everyone close to them.