The temperature is over 100. The rapids are some of the largest in North America. Water levels are rising. And JT Maroney, veteran river guide, is leading his 125th trip down the Colorado River in the Grand Canyon. For the next two weeks, his 13 passengers – strangers, mostly – will paddle, row, swim, ride the rapids, eat gourmet meals, sleep under the stars, and learn a lot about geology. They'll learn a lot about each other, too – perhaps more than they want to know. Allegiances form, and likewise dissolve, in the course of an afternoon. JT's decision on the first day to adopt a stray dog further complicates the group dynamics, leading to a series of fateful mishaps, one of which will alter the course of many lives.