The friends can’t believe their luck when they get to stay in a castle. It’s everything they had hoped for, with a moat and an ancient burial ground that gives it an air of mystery. But things are not what they seem and a treacherous discovery in the grounds reveals a 300-year-old treasure map. The race is on. The After-School Detective Club is in pursuit of Ragnar’s gold, a hoard of treasure said to have been buried by a Viking warrior and guarded by his demon hound…that is, unless someone else gets there first.