NCIS Special Agent Williams is murdered by a professional hit squad in Cyprus, and when the hit man arrives at LAX, NCIS: LA is called in to track his every move and figure out who is the next target.
The hit squad was hired by an infamous Chechen terrorist group whose leader, Vakar, had been presumed dead seven years ago. Williams had been investigating Vakar's death before he was murdered.
Callen and Sam's plans to follow the hitman change when they are spotted and give chase. They bring the hitman into custody and find out that the hit squad is about to rendezvous.
Callen decides to pose as the "B" squad hitman and infultrate the group.
Callen learns that a suburban housewife, Emma Mastin, is the next target.
Sam overhears that the squad members speaking in Farsi and learns that Vakar is actually alive. Kensi and Deeks go to the Mastin home to find out why a Chechen terrorist group would want Emma dead.
Kensi gains her trust and realizes that Emma's son speaks Chechen. Emma volunteers to set a trap for the hit squad in order to send Vakar a message; that it won't be easy to kill her.
Hetty learns that Emma was Vakar's wife and after his staged death, she became a highly trained "Black Widow" who was supposed to become a suicide bomber but escaped.
Her son's father is really Vakar and he knows he needs to eliminate Emma to get his son back. The team takes down the hit squad and Emma personally kills the hitman.