When you watch NCIS: New Orleans Season 2 Episode 15 online, a mentally disturbed man begins shooting up a train full of passengers when a Navy officer and a mysterious Good Samaritan stop him. The Samaritan fatally stabs the man and then keeps the officer from bleeding to death from his wounds before help arrives, but then takes off before anyone can even identify him. The mystery deepens when the NCIS team finally does identify the Samaritan as a corpsman who had gone missing and was presumed dead after being captured by the enemy overseas in 2012. There was no hint that he had even survived his ordeal, let alone that he was back in the United States. It's up to the team to decide whether he's still on the side of angels or whether he's fallen into the pit of evil he had been forced to gaze into during his time in captivity. It's down to a matter of trust, and the CIA is not talking. So do they believe that Corpsman Nolan Griffith is still true to the ideals of the Untied States? Or has he actually become a terrorist himself? Find out when you watch NCIS: New Orleans Season 2 Episode 15 online!