NCIS: New Orleans: The Third Man

The body of Charles Greene, a master diver in the US Navy, washes ashore. The team determines the specialist's body bears signs of a struggle, and a search of the surrounding area brings the agents into contact with former marine Michael Buckley, who had accompanied Greene on his last dive. According to Buckley, the pair's boat was attacked by two people wearing military gear. The case takes a more sinister turn when Homeland Security agent John Russo arrives in town, investigating a report of an imminent threat to New Orleans from a foreign aggressor. Russo's intelligence states a small submarine has been deployed against US interests, and Greene's body bears all the hallmarks of being hit by a similar submersible. Naval crime drama, starring Scott Bakula and Ivan Sergei