On March 8, 2014, Malaysia Airlines Flight 370 vanished over the Indian Ocean with 239 people aboard, and this episode of the National Geographic series uses seafloor mapping and CGI reconstructions to lay out what searchers actually found, and didn't, across years of scanning open water. Investigators and search-team engineers walk through the satellite handshake data that narrowed the plane's likely path to a remote stretch of ocean west of Australia, the debris later recovered on beaches in Reunion and Mozambique, and the sonar sweeps that mapped thousands of square miles of seabed, turning up shipwrecks but no aircraft. The film digitally drains the water to show the terrain search vessels had to navigate, including underwater ridges and canyons that complicated the hunt. It weighs the leading theories, from mechanical failure to deliberate action by someone in the cockpit, without settling on one, keeping the focus on why the most expensive search in aviation history still ended without the plane.