What will the twins get into next? The medieval castle carries centuries of secrets. Hidden deep within... Traveling to Italy, the twins are on vacation until they're not. Strange happenings in the Castello Aragonese d'Ischia draw their attention. When searching for a mystery, the mystery finds them. What happened to the archaeologist deep in the castle's depths? Run for your lives! The ghosts are reclaiming what is theirs. Grace and Henry Warner return with a new folder for the monster case files, a file soon to be filled with clues, facts, and guesses. Join the twins on their journey through a life of travel and mystery with parents who believe in them, as long as they aren't completely sure what the twins are up to.