Border Patrol agents stop a coyote hauling illegal immigrants from Mexico, then they all get gunned down. Hetty is being held prisoner. Deeks and Kensi meet up with his mother and her trainer/boyfriend, but they get called to work. Sam calls in sick on his anniversary. Callen goes to round up a hung-over Sam. At the site of the shooting, Kensi finds a hidden young boy. Mosley gets Enrique to talk by offering him video games to play. Nell's older sister Sydney, who is with Homeland Security, gets assigned to help with the investigation. Callen and Sam check out an abandoned Border Patrol truck, which is rigged to explode. A group of terrorists is in Los Angeles possibly to abduct Ahmed Han Asakeem, who has turned government informer. So NCIS grabs him first. After Callen and Sam get nowhere, Kensi goes in to interrogate him. Eric and Sydney find a suspect, Fazan Kamsour. Sam goes undercover to trap Kamsour by getting him to make travel arrangements for him and Asakeem. Harley sidetracks Aimon Shah, who knows Sam, first by spilling coffee on him, then by taking him out. Callen and Sam flip Aimon. Kamsour calls back Sam and sets up a meet. Mosley goes along as his pretend wife. It's a trap to kill Asakeem, Eventually they take out all the militants. Sydney tells Nell she was hard on her to make her stronger. Sam finds out Mosley has a son, but he lives with his father and she doesn't know where he is. Chegwidden shows up looking for Hetty at one of her houses and Callen catches him. They catch up over drinks. Hetty gets tossed into a cell next to Keane. They commiserate, and she tells him that her people will be coming for her.