The episode begins on an aircraft carrier where two officers get into a fight. The XO is not happy and wants a full report on it. Next, we see that one of the officers is found dead. At the precinct, Kensi tells Deeks that she has no plans this year as she is planning to spend Christmas with her mother. Deeks asks her to get her mom along for snowboarding and also spend some time in his cabin. Nell arrives and tells them that they are being called to the ops. At the ops, Eric tells the team that NCIS special agent Jason Niles who was afloat was found dead and the COD is blunt force trauma.
There is one suspect, Petty officer Simon Allen is an intelligence specialist and according to the last report Niles was keeping an eye on Allen for erratic behavior. Also, Allen got into a fight with Sergeant Jefferies on the day the day the body was found and both men are tested positive for cocaine use. Hetty has arranged for all of them to be flown out on to the ship; looks like Christmas is going to have to wait. Hanna and Kensi are dressed like marine officers and Deeks is a civilian contractor. Deeks is not too happy about his geeky undercover but when he learns that he will have to cut his hair in order to be a marine, he chooses to be a contractor. Sam is not too happy about going on the ship. And it is not Christmas; it is Sidirov that is bothering him.
What if he comes back when they are away? Callen tells him that Michelle will handle him. Next, the team lands on the ship and they are welcomed by Petty officer Smalls. Deeks who is posing as an analyst starts flirting with her. Lieutenant Abernathy shows Kensi the way to her bunk. Callen interrogates Allen and Jefferies. Both of them deny using cocaine. Jefferies says that he doesn’t know Niles and that he learned about him when he was reported dead. Allen tells Callen that he saw Niles just once when Niles intervened in an argument that he was having. The argument was about some music.
Allen then tells him that he was jogging around the deck before the fight took place and that since there was some ongoing work, he was on the lower deck. Smalls is showing Deeks around and he manages to slip away. He then goes to the site where the dead body was found and he finds something. He then ends up in a fight with two seamen and Sam arrives and tells him that he will take it from there. Deeks tells Sam that he found evidence which might indicate that Niles was killed elsewhere on the ship and then his body was dragged down to where it was found. Nell and Eric update Callen about the two officers who got into a fight with Deeks; officer Lambert and Officer Wilson. Also, Lambert worked with Allen for Intelligence.
Deeks then explains to Callen and Sam that he found spinach on the site and it is impossible that it fell there accidentally as the site is on the other end of the ship from where the mess is. But it is even more difficult for someone to drag the body from one end of the ship to another! Abernathy is showing Kensi around when they see that Master Chief is behaving erratically and is trashing down things with a wrench in his hand. Kensi and Abernathy tackle him. But later Sam tells Kensi that the wrench is not evidence as it does not match the wound on Niles’ head. Kensi tells Sam that the chief’s altered state of mind was caused due to cocaine toxicity. The XO is not happy about the allegations against the Master Chief ad he tells Callen that he trust the master chief and that his men are drug addicts.
He then tells Callen that the carrier is a dangerous place and that he should be careful. The four hold a secret meeting. Sam tries to justify the XO’s behavior as his career is on the line and he cannot be blamed. Kensi says that someone smuggled drugs on board and is dealing and maybe Niles was close to find out who is doing this and that might have gotten him killed. Callen points out that all the three of them denied using it. They decide that they might have to search the ship; but that is difficult! So, Callen decides that if he portrays that he is getting close to the person dealing in drugs, maybe the perp would get nervous and make some mistake. Callen interrogates Master Chief Brown, and Brown tells him that he does not drink, smoke or do drugs. He has to set an example for those under him.
He says that there is no way he can explain his violent behavior. At the ops, Nell has brought some elf’s costume for Eric. But Eric refuses to wear it as he thinks it would be disastrous if Sam, Callen or Deeks saw him wearing it. Nell wanted to do this for the children and she is now upset. On the ship, Callen tells Sam that Brown has the cleanest service record he has ever seen and he feels that someone is trying to set him up. Deeks is still snooping around and he finds Lambert is fixing the refrigerating system which keeps crashing. Deeks goes to check the stores. He sees the pipe valve and assumes that Niles could have hit his head on that. He clicks pictures and just then someone comes from behind and tries to choke Deeks. Deeks is unconscious and he collapses to the ground and the man (whose face is not shown) runs. Eric tells Sam and Callen that he is not able to get in touch with Deeks. And he also confirms that the picture that Deeks sent him match the murder weapon. Callen tells Sam to alert Kensi. He then goes to Brown as he feels that the Master Chief knows the ship the best.
They arrive at the site where Deeks clicked the pictures but there is no sign of Deeks. Sam questions Lambert and Lambert tells him that Deeks was snooping around a while ago. Just then they see that the guy who was supervising the refrigeration repair is walking away with the trash can and he doesn’t stop despite being asked to. A gun fight ensues and the man is killed. Deeks falls out of the trash can. But there is still no sight of the drugs. Deeks says that the refrigeration was being tampered with so that the veggies could rot and this could throw off the K9s. but Sam knows that this is not easy. They then check a wall and it is freshly painted. Callen scrapes off a bit and finds that the cocaine is mixed in the paint! These guys are good!!
Next, Eric educates the team about the dead man; his name is Leonard Wall. He is a contractor and he used the Navy to move his drugs. Case Closed. Next, Eric tells the team that he has managed to get tickets only for the 27th of December and this means that they are going to have to spend Christmas in the sea. Hetty is off for vacations and there is nothing Eric can do to help. On the ship, Brown thanks the team for all their help. Just the Hetty arrives. She was on her way to her vacation spot and she decided to make a pit stop. She has made arrangements for only for Sam so that he can go back to Michelle and spend his Christmas with her. He is ecstatic. He sweeps Hetty in his arms a kisses her. He leaves.
Everyone is happy for Sam. At the office, Eric is unhappy to see the empty precinct. Nell arrives wearing her elf costume. She then kisses Eric; well they are standing under the mistletoe. She wishes him happ holidays and is about to leave. Eric rushes to get his elf costume. The episode ends.