How can you tell if a river's under a spell? River trolls, rock trolls, blue-wing fairies-the usual suspects. The stretch of the Mississippi where Claire lives has rumors of them all, not that she's ever spotted any. But then Claire's cousin Duke takes a swim and sprouts a horn-a long, pointy, handsome thing. After that, Claire doesn't have much choice but to believe that something rivery is going on, especially since she's the only one who can help...