Cam Jansen: the Mystery at the Haunted House #13 by David A. Adler

No mystery is too great for super-sleuth Cam Jansen and her amazing photographic memory! Mysteries follow super-sleuth Cam Jansen everywhere she goes...even to an amusement park. Cam, Eric, and Cam's aunt Katie and uncle George have just braved the amusement park's Haunted House when Aunt Katie realizes that her wallet is missing. Did she lose it or was it stolen? Cam is convinced that this is the start of a very spooky mystery! The Cam Jansen books are perfect for young readers who are making the transition to chapter books, and Cam is a spunky young heroine whom readers have loved for over two decades.