The team welcomes Gregorio with her own NCIS hat. The body of Lt. James Nielsen was found by deep-sea fishermen. With Sebastian struggling in NCIS training, Loretta is having to make do with temporary assistants. LaSalle, Percy and Gregorio find Nielsen's boat, where he was killed. The stolen boat's last trip was to a deep-sea oil rig. Sebastian suggests that Nielsen was killed with a welding torch. Pride goes to the rig to investigate. Darren Meade, Nielsen's brother-in-law, is a welder, but the team has no way of reaching Pride to tell him. Pride is interviewing Meade and Meade attacks him with his torch before Pride gets away. Pride finds out that other crew members, Jackson Hauser and Lyle Peterson, are involved in sabotaging the pipeline and that he's on his own. Meade attacks with Pride's gun before Pride fends him off with a flare gun. He's helped by Bonnie Madigan, who directs him to the emergency beacons. They discover the gas leaks are building to a huge explosion. Sebastian gets in trouble during training for receiving calls from the team. Pride broadcasts a message in Morse code from the rig about the potential explosion. The remaining team members discover that someone on land is helping the saboteurs -- the owner's son. Sebastian leaves training to help save Pride and the rig. Pride surrenders himself to the roughnecks so he can explain the dire situation to them and Madigan escapes through the ventilation system to get the other crew members off the rig in the lifeboats. Sebastian remotely walks the quartet through the procedure needed to prevent the explosion. Madigan comes back to rescue Pride and arrest the trio. After observing Sebastian in action, Perkins the training agent lets him back in the program.