Kelsey's dad has a new job and that means a new house―on the same property as a castle! Kelsey, Becca, and Leo can’t wait to explore, but what they find might lead to their most intricate case yet. How are an abandoned tree house, a wad of cash, a missing heirloom, and a mysterious creature roaming the grounds all connected? The Curious Cat Spy Club is determined to find out! Linda Joy Singleton is the author of thirty-five books for children and young adults including YALSA-honored The Seer series and the Dead Girl trilogy. She lives in California.