I first read Eager's books as a child and I have been reading them on and off for the last twenty-five years (I keep a complete collection in my bedroom and I read them whenever I want a good laugh).
Eager writes on two levels--there is something in this (and all of his books) for both children and adults. As a kid, I loved Roger, Ann, Eliza and Jack because they aren't perfect and because they have their own squabbles and flaws. As an adult, I find them refreshing in their honesty---Eliza, especially, always lets you know how she feels!
The story is wonderful and begins with the scenario of all great children's books (missing or distracted parents). Roger and Ann's father requires emergency surgery and the family travels east to Baltimore for the operation. A visit to Aunt Katherine's is to be dreaded b/c of cousins Jack and Eliza (as Ann puts it "Jack and Eliza---help!). Jack is camera-obsessed while Eliza was the bossiest nine year old on the block before she moved to Baltimore.
But...a magical gift from Uncle Mark brings the cousins together. A castle complete with all the characters from Ivanhoe comes magically alive every three nights and Jack, Eliza, Ann and Roger are soon embarked on a variety of quests. Somehow tho' nothing seems to work out quite as Roger, Jack, Eliza and Ann plan---Ivanhoe is nearly captured when Roger spills the beans about his hidden presence in the castle, an attempt to modernize 'ye merrie England' results in Ivanhoe's experimenting with space travel and so on. Gradually, Roger realizes that he needs to perform a great deed if he is to help his father recover and he, Ann, Jack and Eliza draw on their own inner strengths to perform the necessary quest and save chivalry for ever.
Don't miss out on this book! Half Magic, Magic By the Lake (which deal with Roger and Ann's mom and her siblings) and The Time Garden (which features Jack, Eliza, Ann and Roger) are among the best children's books written this century. I won't compare them to the Harry Potter books (equally great!) but I will say that if you loved Harry Potter, you will love Edward Eager.