On a beach a Marine spots a decomposing body; Gibbs and company investigate; at the scene Duckman spots a round penetration in the victim's wet suit. McGee identifies the diver as a Navy lieutenant on leave. While Gibbs and Tony check out the vic's home, they meet two agents of the Coast Guard Investigative Service (CGIS). Abigail, the CGIS agent in charge, and her probie present certain similarities to the gang. Gibbs and Abigail agree to work together; a CGIS lab tech suggests that they may have a double homicide. Gibbs and Abigail barge into a scrub room but fail to find the right surgeon, so Tony and Abigail talk with the wife of the missing physician. Ducky raises some medical questions about the identity of the dead diver, and Abby makes a revealing discovery, then Gibbs, Abigail, and Tony reach a conclusion and bust the bad guys. Tony meets Miss Biloxi, Ducky reverts to bow ties, and Tony and Ziva catch a pirate flick together.