The Haunted Hotel by Janet Adele Bloss, 1989.
Laura and Bill are visiting their Uncle Joe, who is the caretaker of a large hotel in New Hampshire. The hotel is closed for the winter because it is too old and poorly-insulated to heat. The children think that the big, old hotel is fascinating, especially when they begin hearing stories about the ghost of a princess who is said to haunt the hotel and put people under her spell to do her bidding. It’s just the sort of thing that Laura reads about in her favorite series of mystery books, and she’d love the chance to investigate something like the heroine, Gwen Gilderstar.
Bill rolls his eyes at Laura’s melodramatic mystery obsession, but then the children begin noticing that their uncle is behaving strangely, and they start to wonder if he is under the princess’s spell. When they first arrived, their uncle told them that his sister, their Aunt Gigi, had gone away to visit a sick friend. Then, Laura overhears him talking to Gigi on the phone, saying that she and her brother and parents went out to dinner, so she can’t talk to them. Later, Laura gets the chance to talk to Aunt Gigi and finds out that she only went to visit her friend because Joe insisted and that her friend isn’t sick. What is going on? Why would her uncle lie? Is he under the princess’s spell?
Laura and Bill see mysterious lights and a shadowy figure in the windows of the closed hotel. Could that be the ghost of the princess? Even though their parents have forbidden them to go inside the old hotel, the kids go there to investigate. They hear organ music and a woman laughing, and they find a red rose on the floor, just like the roses in the portrait of the princess. Then, Bill catches a glimpse of the princess in the elevator, carrying a silver axe! Laura is determined to solve the mystery, just like Gwen Gilderstar. She’s afraid, but she knows that she has to something for her uncle’s sake.