The cave at Mount Bonnell, not far from the school Hannah, Nick, and Jackie attend in Austin, has attracted many visitors over the years, from Indians to Boy Scouts to historic reenactors. But when Jackie's grandfather takes the trio there on an impromptu excursion, they meet a traveler of an entirely different sort: explorer Elijah Barrington, who has arrived there from the past. And accompanying him is a trunk that looks oddly familiar. A slam of...