ALA Booklist

In a sequel to The Castle in the Attic (1985), William receives a magic token for his birthday, along with a note about love, courage, and loyalty and a reminder that his new age, 12, is appropriate for becoming a squire. Since this same token whisked him back to medieval times in the previous episode, William and his friend Jason try it again and, entering the castle in the attic, find themselves caught up in a wild drama involving an ancient chant that foretells the return of evil. Along with young Gudrin and her Uncle Dick, among others, William and Jason lure hordes of deadly rats into the castle while they wait for Sir Simon to return and rescue them. This well-crafted story is a beautifully blended mixture of fantasy and adventure, with a forceful and thoughtful underlying theme of courage. Readers who have not read the first book will find this story satisfying on its own, and many may clamor for further adventures created through the powers of the small token. (Reviewed Sept. 1, 1993)

Horn Book

In a satisfying sequel to 'A Castle in the Attic' (Holiday), William receives a magic button that allows him and his best friend to return to his castle and rescue the inhabitants of the tiny kingdom from an army of enormous, destructive rats. The engrossing story combines adventure, villains and heroes, and subtle introspection about the need to be valued.

Kirkus Reviews (Thu Apr 28 00:00:00 CDT 2022)

Now that William is 12, housekeeper Mrs. Phillips—who, two years ago, gave him the Castle in the Attic (1985), where they shared an adventure before she went home to England—sends William the magic token he believed she had destroyed. Stung by his failure to perform a dangerous initiation rite—jumping a freight train, a tradition for local 12-year-olds—William shows best friend Jason how the token can change their size. Miniaturizing each other, they enter the world of the castle, where William gets a hero's welcome in honor of his earlier exploits and the two, with the help of a girl their age, avert a new threat: an army of human-devouring rats led by a mesmerizing giant rat. Including just enough details of setting and character to give her story texture, Winthrop keeps it moving with some humor (there's a witty jester, rather underemployed here, and a joust between a pompous knight and Jason, with a lance, on his bike); some mild horror involving the rats and a fortuitous twist leading to their defeat; and the kind of compromise between courtly and colloquial dialogue that imaginative children make in their dramatic play. No one changes much, but William does make the sensible decision, before he gets home again, to give up on the train. Accessible, well told, and entertaining. (Fiction. 8- 12)"

School Library Journal

Gr 5-8-- Two years have elapsed since young William battled the forces of evil in The Castle in the Attic (Holiday, 1985). Now turning 12, he's miserable because he thinks his friend has outstripped him in bravery, for Jason has ``jumped the trains,'' which is the local male rite of passage, while he has failed. In the previous story, his family's former housekeeper gave William a model castle and a magic token through which he entered its inner world. Now that he is maturing, she again presents him with the token, and he and Jason return to the castle. William is welcomed back and he soon learns that there is again great danger in the land. A monstrous army of rats, behind a gigantic leader, is ravaging the land, eating everyone in sight. William is pressed into defending the castle and destroying the rats. He has to rely on his wits and his courage, for the magic token has been stolen; in the process, he learns that he does not have to jump trains to prove bravery. William and Jason offer contrasting models of what constitutes heroism. Some readers will wonder how the rats came under the spell of their demonic leader, but others will just enjoy the adventure. --Virginia Golodetz, St. Michael's College, Winooski, VT