At a mall a couple of suspects dressed as Santa Claus attempt to flee from the LAPD. One of the men takes a hostage, but eventually turns himself in.
Sam contemplates going out of town for the holidays, but wishes he could see his wife and kids. He has to stay with his wife's younger sister.
Billy Rex, the suspect that was caught, was apparently attempting to steal a computer virus. Sam and Callen are instructed to stay away from the crime scene because the woman that was taken hostage was Joelle Taylor. Instead, Deeks and Kensi interview her.
Billy escapes from custody as Kensi and Deeks go to interview his target at the security firm - Weber. They uncover that Billy stole malware that could be incredibly deadly if in the wrong hands.
The gang gets a line on the other men dressed as Santa - a motel. Nell cancels on her plans with Eric for the holidays, but they push that aside when Eric discovers that the stolen malware targets electric grids specifically. It could shutdown the country's grid.
Deeks puts his foot in his mouth when asking Kensi to join him on a ski trip, but they try to work through that moment of awkwardness.
Sam and Callen talk to a bookie that used to be Billy's boss. He ties Billy to a previous murder, but says he doesn't know where Billy could be.
Meanwhile, Kensi and Deeks find the other Santa's at a motel, apparently drinking the night away.
Leroy and Stu come to agreement that Rex was the one that target the computer equipment, while they were there for a regular break in.
Tate, the bookeeper, was being hacked by Weber, but before Tate's account could tell him about the malware attacks - he told Billy. This lead to Billy killing Tate's accountant then attempting to steal the software himself.
They deduce that Billy planted the drive onto Joelle, and Callen finds a way to retrieve successfully.
Hetty uses her prowess to get answers out of Weber - they find out that he was involved with setting up the robbery due to being afraid of Billy.
Callen remains at Joelle's house for protection. Billy arrives with another man and forces them to evacuate.
Callen secures Joelle in another house and warns her to stay in place. He gets into a shootout and scuffle with Billy but manages to gain the upper hand.
With the thumbdrive in place, Callen turns his attention back to his girlfriend.
Joelle does't take well to Callen's revelation and they part ways for the time being.
Deeks, Kensi, and Callen go ice skating with Sam and his family. Kensi and Deeks bring up their relationship and decide that it is finally time to stop playing games and try to make the transition to the next level. Sam is surprised by his son, who's recently been promoted to cadet sergeant, and couldn't be more proud. Lastly, Joelle gives Callen a surprise of her own when she visits to patch things up.