Knight’s Castle by Edward Eager, 1956.

Roger and Ann are the children of Martha from the previous two books in the series. Like their mother’s family when they were growing up, they live in Toledo, Ohio. Their Aunt Katharine (one of Martha’s older sisters) used to live close to them in the Midwest but now lives in Baltimore, Maryland. Roger and Ann don’t particularly get along with Aunt Katharine’s children, Eliza and Jack, because Eliza is bossy and Jack is only interested in photography. However, the four children end up spending the summer together when Roger and Ann’s father needs to have an operation at a hospital in Baltimore.

Like their mother and her siblings when they were young, Roger and Ann also like fantasy stories, which their father likes to read to them. Roger starts to believe in real magic when it seems like one of his toy soldiers comes to life at night. Roger collects toy soldiers, and he has over 200 of them, but this one is special because his father says that its been handed down in their family for generations. Roger calls it the Old One. It’s rather worn, so it isn’t obvious at first, but the Old One is actually a knight. Worried about his father’s illness, Roger takes the Old One to bed with him (which he thinks is more manly than taking a teddy bear to bed), and then feels it wriggling in his hand.

Realizing that the Old One is magic and is coming to life when he holds him, Roger asks him if it’s part of his magic to grant wishes. If it is, then he wishes for his father to get well, and if possible, for him and his sister to have an adventure in Baltimore over the summer. The Old One doesn’t answer him immediately, but over time, he makes it clear to Roger that wishes have to be earned, and that will be the source of his summer adventure.

When the children arrive in Baltimore to stay with wealthy Aunt Katharine while their father is in the hospital, Aunt Katharine gives them presents. Ann gets a new dollhouse, and there is a toy castle for Roger. Since Aunt Katharine has also just taken all the children to the movies to see Ivanhoe, all of them become immediately interested in playing with the castle.

That night, Roger has a strange dream that he finds himself within the story of Ivanhoe, which is being acted out in his toy castle. The Old One is there as well, although he is mainly watching the action as Roger begins to take part in the story. When Roger comes face-to-face with the villain, he accidentally lets Ivanhoe’s plans slip to him. Things are looking pretty bleak when Roger suddenly realizes that the castle is still a toy and everyone around him is just a lead soldier. This revelation ends the magical adventure and brings him back to reality. However, Roger is disappointed that he ended the adventure so early when perhaps he could have done something really heroic.

Seeing the toy soldiers scattered around instead of poised for the battle they were planning the night before, Eliza and Ann think that Roger was just playing with the castle without them, but he explains to them what happened. The girls were just reading The Magic City by E. Nesbit, and they start building their own “magic city” out of random things from around the house, surrounding the toy castle. Roger is upset about the city because he says that it doesn’t fit in with the Ivanhoe story, and he’s sure that it will ruin everything, maybe from preventing the magic from working again at all. The Old One tells Roger that magic works by threes, so the next opportunity for magic will be in three days.

As it turns out, the city does end up becoming part of the story when the magic brings it all to life on the third night. Roger, Ann, and Eliza find themselves in the middle of the city, surrounded by knights attempting to drive modern cars. Ivanhoe has become a fan of science fiction books, via the public library in the city that the girls built. Although Ivanhoe has turned into something of a geek, the children persuade him to come on a mission to rescue the captive Rebecca, and they end up traveling in a flying saucer (made from a real saucer) to the Dolorous Tower, where the adventure ends as soon as Eliza remembers that the villain threatening them is still just a lead soldier.

It was an even weirder adventure than Roger’s first one, but by now, the children are starting to understand the rules that go along with the magic. Jack, who says he doesn’t really believe in magic, accompanies the other children on the next adventure, as they try to prove to him that it’s real. They end up having to rescue some of the others from the “giant’s lair”, which turns out to be Ann’s new dollhouse. The dolls are angry that Ann has been neglecting them, only paying attention to the dollhouse when she and Eliza needed to borrow things for their magic city. They manage to escape again by remembering that the dolls are just dolls.

However, Roger is still worried about their father, who is about to undergo his operation. The Old One had told him that wishes needed to be earned, and he doesn’t think that they’ve managed to accomplish much in their adventures. Roger thinks that they need to do something really heroic so that his wish for his father to get better will come true. The Old One gives Roger a rhyme, hinting at what the children need to do on their next adventure, but Roger doesn’t understand what it means, and he doesn’t know if he can figure it out in time.

Actually, it is Ann who eventually realizes what the rhyme means and provides Roger with the “wisdom” that he needs to earn his wish. All throughout the story, Roger was criticizing his little sister for things she did wrong, saying that she was too little and only a girl. Because Roger thinks of her as being just his little sister, he overlooks what she has to contribute to the adventure. Roger’s acquired wisdom is to value the contributions of others and not underestimate their ability to contribute. Ann, being young and shy, frequently doubts herself, but she also learns confidence when she realizes that she has the answer to the riddle. Jack and Eliza learn lessons as well. Doubting Jack learns to believe in magic, and Eliza learns that she can’t always be the boss, that sometimes it is better to let someone else take the lead when they’re the right person for the job. (Although, she does say at the end of story, “If that wouldn’t be just like that magic’s impudence! Trying to teach me moral lessons!”)

Like other books in this series, there are a lot of references to popular pieces of children’s literature and jokes about things that happen in children’s stories.

The book is currently available online through Internet Archive.