Details the reunion and subsequent adventure of the Blyton Summer Detective Club, now adults, as they confront a supernatural mystery in their old stomping grounds of Blyton Hills. The narrative follows Andy, Kerri, and Nate, accompanied by their loyal dog Tim, as they investigate strange occurrences linked to a past case involving "Sleepy Lake creatures" and the enigmatic Deboën Mansion. Through their investigation, they uncover a deeper, occult plot involving an ancient entity and a necromancer, forcing them to revisit unresolved trauma from their youth while battling monsters and personal demons. The story culminates in a desperate struggle to save the town from a looming apocalypse, revealing secrets about their past and testing the bonds of their friendship and love.