Phil and Jess search whitewater rapids and a frigid Alaskan lake for a legendary beast that's now the target of serious scientific inquiry. Armed with new eyewitness accounts and advanced underwater robotics, the team takes a deep dive for answers.

Braving shark-filled waters and deadly undersea tunnels, Jess and Phil probe reports of the Lusca, a sea monster said to be attacking Bahamian locals. Their hunt takes them deep into unexplored "blue holes" -- and could expose shocking military secrets.