Knock knock. Who's there? More trolls to add to Brett's (Christmas Trolls; Trouble with Trolls) canon. Apparently, the trouble with trolls is that they're always making trouble. Luckily, they never get any smarter. In this Arctic story, a shy Finnmark girl fends off lurking trolls with help from a traveling boy and his pet polar bear. An icy landscape shimmers under the northern lights while bright Scandinavian frocks and household items give the scenery a kicky dash of color. Brett simultaneously reveals another angle of her tale via intricately designed side panels that frame the main event. The lifelike polar bear, both hulking and docile, is a scene-stealer. Ages 4-8. (Sept.)