When colleague Dora Simpson asks Frankie MacFarlane to fill in as geology professor on a whitewater trip hrough the heart of the Grand Canyon, Frankie jumps at the chance. Eight days. Nearly two hundred miles on the river. One mile deep into the earth. What could go wrong? Everything. Frankie wrenches her knee on the first day. On the second, a solo kayaker forces her to choose between being gutted by a Bowie knife and drowning in the frigid water...