An author of splendidly complex, challenging thrillers (Wolf, 1990, Carnegie Medal) sets a picaresque adventure in 19th- century America. Orphaned Tad, 15, drudge at his aunt's boardinghouse, quickly accepts Michael Keenan's offer of work caring for his elephant, Khush; Keenan travels about selling a cure-all falsely advertised with a trick involving Khush and Keenan's daughter Cissie. After Keenan dies in a train wreck, two rogues from Tad's past claim Khush. Sure the bill of sale is forged and that, somehow, Cissie's friend Ketty (who lives in Nebraska with her new husband) can set things right, Tad and Cissie set out, with Khush, to find her, traveling the Ohio from Pittsburgh to Cairo and then upriver and across country to the plains west of Omaha, the claimants in hot pursuit. Their escapes and rescues, encounters (including one with a utopian community) and transportation are well varied; along the way, the bossy, querulous Cissie and self-deprecating Tad gain in self-knowledge and build an affectionate relationship, while Khush is consistently intelligent and endearing. There's a suspenseful race to the finish and a satisfying number of surprises, all duly presaged, when Ketty is found. Cross's Midwest is less persuasive than her British settings, but it's authentic enough; the adventure is the main event here, and that's grand, old-fashioned fun. The book has won Britain's Smarties Prize. (Fiction. 10-14)