As Carolers sing at the doorstep of a home in a quiet L.A neighborhood, gunshots ring out and the bloody figure of a man appears at the door and two men are found shot to death inside.
The team is called in when the identity of the bloody man is discovered to be a former Navy Intelligence agent, Brett Talbot, who suffers from PTSD.
The team must figure out who killed the two men in his home and do the murders have anything to do with Talbot's intelligence work in Afghanistan.
The team speaks to Talbot’s psychiatrist who tells them Talbot's PTSD is crippling to his life; this resonates with Kensi.
In order to help Talbot remember what happened the night of the murders, Kensi divulges to him that her former fiancee also suffered from PTSD and she tried but could not help him.
They take Talbot back home to try and jog his memory but he panics and starts to regress and suddenly admits he killed both men in self-defense after one man, a drug dealer, shot the other man, Talbot's nurse.
Kensi grows closer to Talbot which almost gets her killed when the Iranian Secret Police try to shoot her to get to Talbot.
As Sam and Callen dig deeper into Talbot's past, they find a former fiancee who tells them Talbot is a sociopath and pathological liar.
They relay the info to Kensi and Talbot catches on, attacking her, but Deeks fires at Talbot who gets away.
A chase ensues and the team realizes Talbot faked his PTSD to have an alibi when he sold his intelligence secrets to the Iranians.
His nurse caught on to his plan and brought a drug dealer friend to try and strong arm Talbot into giving them a cut so he killed them. Kensi catches up to Talbot first and must put her feelings aside and takes the shot, killing him.
Hetty surprises everyone by giving them Christmas gifts. The real surprise comes when they all open them and realize she has re-gifted presents all of them have given her over the years.