The eight explorers are on the fourth leg of their expedition and are struggling to stay afloat on the Talachulitna River. With currents rushing at dangerous speeds, it’s no easy feat to navigate the frigid waters. Expert climber Willi Prittie teams up with Iditarod champion Dallas Seavey and his brother Tyrell to find a much-needed food source. Meanwhile, mountain man Marty Raney and his son Matt enter the river further downstream hoping to minimize their time on the water.