On an ordinary Monday, Rill Kruse left for third grade with a dad, but when she came home, he'd been stolen. By a river. One year and thirteen days later—on the first morning of summer vacation—Rill still insists he's trudging home. Her mom has become a practical woman. Her older brother, Eddy, now calls her baby and dork. Gus, second-in-command at Kruse Whitewater Adventures, Rill's family's rafting company, has gone from being her dad's "risk bro" to her mom's guardian angel. Joyce, company secretary, arm-wrestler, and mechanic, still calls Rill a fingerling, but, after learning what a cheater water is, Rill wishes she'd stop. When Rill's cat, Clifford, leads her to the family tree fort on the mountainside behind home, she discovers a stowaway, Perla. To help Perla, Rill embarks on an adventure that tests her understanding of the world, of loss, and of what it means to be a friend. In the end, what Rill discovers will nudge her—and all those she loves—toward healing.