Jess loves thunderstorms and can be counted on to take a strange dog in stride; her older sister Claire—blessed with what her dad terms ``an overactive imagination''—``bleats'' at a tree's windy heights and anticipates a shot as ``a dagger,'' not the ``mosquito bite'' the doctor promises. Still, it's Claire who listens avidly to Grandpa's tales of Harriet Tubman and William Wilberforce and enjoys reenacting their bold deeds; and when bullies snatch Jess's beloved ``Pink Ted,'' Claire boldly saves the day with an impromptu story about two dauntless cousins, Wellington and Wilberforce, heroic products of that same overactive imagination. In her appealing full-page paintings, Wilson catches every nuance in the believable interaction between these deftly characterized little girls. Told with vigor and gentle humor, an unusually fresh look at a perennially interesting theme. (Picture book. 3-8)