Sam's former contact and "brother", Moe, is attacked in prison. Sam and the team rush to his aid to help figure out why someone would want this model prisoner dead. They discover that Moe was beaten as an initiation into a well known and highly secretive terror group that has members in the prison. Entities within NCIS told Moe that if he got close to the leader of the group they would get him out of prison. Sam comes back to the team with this info and Hetty surprises them all when they find out Nate is already placed in the prison watching over Moe. Sam also goes undercover to get close to the prison's group leader and find out what the group is planning and to protect Moe. As they dig further they realize the group was working with a prison guard to create an escape plan to get the terror group leader's brother, Abdul Habaza, and his lieutenants out of prison and back to Yemen to lead the terror group in planning a massive terror attack on the U.S. Sam and Moe know they must help Abdul escape in order for them to track him, using Overwatch, and gain intelligence on this previously impenetrable organization. Unfortunately the assistant warden is dirty and is about to expose Sam, Nate or Moe as agents to Abdul so they must put the escape plan into action immediately. Moe assists the team in the escape but pays the ultimate price when Abdul tortures and kills him for information on the undercover agents. Moe covers for Sam and Nate to the end and Sam is determined to avenge Moe's death one day soon.
Callen gets a clue to his past and Hetty allows him to leave to pursue it.