Deeks, Kensi, Sabatino, and Wallace overcome a first ISIS attack on the CIA bunker in Iraq. ISIS sleeper agent Michael Skinner is barricaded aboard the USS Allegiance and has killed three American sailor hostages. The false-flag attack on Tel Aviv and Riyadh is stopped. Hetty, Mac, and Fatima are heading to Saudi Arabia, trying to head off retaliatory strikes. The quarter in Iraq uses an escape hatch then blow up the bunker with the ISIS reinforcements inside. Sam and Callen capture Skinner and rescue his remaining hostages. The only ones who have proof of the false-flag attacks are Alexandra Duvivier and Muhammad Pliyev, who need to be located. Sam, Callen, and Harm unsuccessfully interrogate Skinner. Harm and Mac reunite for the first time in nine years in Riyadh, while the NCIS team gives them privacy. Callen and Harm meet with Mossad Agent Elianna Sapir, one of Callen's exes. Sam and Fatima go to Tehran to approach Laleh Ayari, to get information to her estranged father, an influential mullah. Hetty and Mac meet with Prince Kamal about the missile launches but he needs proof. The Iraqi quartet capture a pair of truffle hunters, who had given their ATVs to Duvivier and Pliyev when the ISIS fighters showed up. Mac and Hetty call Kensi looking for proof. Etlianna takes Harm and Callen to meet with an Israeli fixer and a brawl ensues. The quartet rescues Duvivier and Pliyev from Isis fighters about to kill them. They upload the information to Hetty and Mac. Hetty puts together a feast for everyone. She suggests Harm apply for an NCIS leadership post in San Diego. Mac and Harm come to terms with their past. Hetty tells Sam and Callen they're staying for a special mission while the rest fly back.