State Troopers pull over a drinking and driving Agent Fornell.
Fornell tells Gibbs he had only just cracked the bourbon, and that his condition was a result of a beer at supper plus some pain pills.
Vance calls Gibbs to a the scene of an explosion which took place on a ship, killing one and injuring six others. On board were dignitaries from a dozen international agencies who were there to attend a summit on global terror.
The team discovers bomb fragments indicating that the explosion came from a Russian grenade.
Russian councilor Anton Pavlenko shows up on the ship to speak with Gibbs and Vance, who accuse him of being conveniently absent until the danger was over. Pavlenko objects, claiming that he too is a target for Mishnev. His reasoning is that Mishnev is angry at him for providing help to Gibbs after the helicopter crash, and that he has therefore become a target.
Gibbs is irritated and he snaps at the team. Tony confronts him and suggests that he and Bishop can handle the witness interviews. Ducky backs him up.
Emily Fornell contacts Gibbs and asks him to help her self-destructive father. He agrees to do so.
The team is briefing Gibbs on their progress when Fornell shows up smelling of booze and offering to help in the investigation.
Vance calls Gibbs and Fornell into his office. Fornell demands to be in on the operation, particularly if Mishnev is involved. Vance asks him to wait outside while he speaks with Gibbs.
Gibbs offers to let his team run the investigation while he takes himself and Fornell out to his cabin. He tells Vance they are both too close to the case. Vance agrees.
Gibbs and Fornell head to Gibbs' cabin. Fornell think Gibbs is performing an intervention, but Gibbs gets out some booze and invites him to kill himself with alcohol and offers to go along for the ride.
Gibbs, Tony and Bishop interview some of the survivors at the hospital.
McGee interviews Frankie Goulos - a sound technician hired to assist with the remote hookup with SecNav for the summit.
Bishop reveals to Tony and McGee that Gibbs had asked her husband Jake to share any and all NSA intel regarding Russian-Palestinian relations, Sergei Mishnev, Anton Pavlenko. She says that Gibbs called Jake that morning and instructed him to share all of the intel with the NCIS team.
Gibbs dunks all of the booze. Fornell says he's done. He punches Gibbs in the face, and when he tries again Gibbs pushes him out of the door. They have a discussion about Diane.
Pavlenko meets Sergei in an alley. He offers Sergei a proposal from the Russian government: asylum and complete immunity from charges, but on one condition: he must kill Gibbs. He tells him it must happen today. He says his people know exactly where Gibbs is.
Pavlenko also reveals that the scientist that Gibbs pretended to kill in order to save his life was a ruse, and that's she's still alive. He tells him that Gibbs did that so the scientist could defect to America.
The team discovers that Sergei was born in Israel to a mother who was a Saudi national with Palestinian roots. His father was a Russian officer stationed there. His father took him back to Russia and left his mother behind.
The team explains to Bishop that Ziva David had a half-brother - Ari Haswari - who was also born to a Saudi mother. They theorize that Ari and Sergei were half-brothers, which explains the depth of Sergei's hatred of Gibbs.
Abby tells Vance and McGee that the trigger for the grenade was set to a sound frequency, and that it may have been implanted with the sound equipment.
Fornell tells Gibbs that he and Diane had a fight before she died, where he said he thought their rekindled romance was a mistake. He said that she had called him before going to meet Gibbs, saying that she didn't think it was a mistake. It was the fact that she died thinking he didn't love her that was haunting him.
Gibbs, Bishop and Tony re-interview Boulos in his hospital room. They show him a picture of Sergei who he seems to recognize. Boulos' father enters the room, sees the photo of Sergei and drops the food he was bringing to his son.
Tony calls Gibbs to tell him the news, but the phone call gets cut off. Fornell wants to go back, but Gibbs says they're not done yet. Gibbs noticed that his cell phone has no reception. He checks Fornell's cell phone - with the same results.
Tony and Bishop interrogates Nazar Boulos, who says he and Mishnev played together as as boys in Palestine, and that they reconnected as young men in Kabul. He says Mishnev walked into his shop last week. Mishnev knew Boulos had been contracted by the Navy and insisted he help him deliver a package. Mishnev placed the package in the speaker while assuring him his son would be safe. He says he doesn't know where Mishnev is, but mentioned that he had seen him today.
He says that Mishnev wanted a cell jamming device.
Mishnev bursts into the cabin and sees only Fornell. Gibbs sneaks up behind him and hits him over the head with a block of wood.
Mishnev awakens to find a gun. Fornell confronts him. Mishnev points his gun and pulls the trigger but it clicks empty. Fornell shoots him dead.
Gibbs is at home when Pavlenko enters. It turns out he and Gibbs had formed the plan for Mishnev to confront him.