The Castle Key

Twelve year-old Moon lives with her father after the mysterious departure of her mother. She leaves Moon with nothing but a beautiful ring, which also mysteriously vanishes. Moon, who yearns to see her mother again, believes strongly that someday she will. She develops an interest in magic as a way to find her mother and her friend Duncan is eager to assist. Her breakthrough comes when she finds a curious key in the office of the school librarian. When Moon touches the key, she becomes an invisible observer in the middle ages.