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)