Martha's children, Roger and Ann, and their Aunt Katharine's children, Eliza and Jack, find that the combination of a toy castle, Scott's Ivanhoe, and a little magic can build another wonderful series of adventures. A running theme in Eager's novels is his many references to the novels of E. Nesbit; Knight's Castle pays explicit tribute to Nesbit's The Magic City, and also makes an explicit reference to the cartoons of Charles Addams. (Half Magic includes a reference to a short story by Saki.)