The Mystery at Windemere Mansion. Kid Detectives, #13

Julie Kostas, one of the kid detectives, is staying with her Aunt for the school holidays, at Windemere Mansion. The Mansion is so filled with paintings, antiques, and artefacts, that her Aunt finds it difficult to keep track of everything. She does begin to notice though, some of the valuable items are disappearing. The Police will be called in. Julie asks if she and her friends can also investigate the missing items.
The Aunt agrees and Julie puts a call into Jason and Luke, the other kid detectives, to come and stay at the Mansion while they look into the mystery. Strange things are happening in and around the Mansion at night. The kids are having to stay up all night as they try to track the movements around the Mansion at night. Figures who are followed seem suddenly to vanish into thin air. The kids begin to make progress when Julie's Aunt tells her of an old book about the history of the Mansion in the library.
The kids are hoping the book might give them answers to the mystery at Windemere Mansion.