When colleague Dora Simpson asks Frankie MacFarlane to fill in as geology professor on a whitewater trip through 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. Frankie chooses the river. Who wants Frankie dead? And why? As Frankie searches for answers, she discovers that one of her students is traveling incognito, fleeing a forced marriage. Has the Family tracked Molly into the Canyon? How can she escape when the few exit routes will be watched? The threads come together at Phantom Ranch, the only place in the Canyon where bridges link trails descending to the river from the North and South Rims. But will ecoterrorist wannabees bring down the bridges before anyone can escape? With the riveting suspense and acute attention to geological detail that readers have come to love, Frankie faces the Colorado River rapids and the perilous mystery at hand with courage, skill, and ingenuity.