A cargo delivery truck (similar to UPS) drives up to a military facility. A female driver gets out and the two guards make her unload the box she's delivering. They check it with a scanner to see if there's anything radioactive or bomb-associated inside, then open it to find the body of a man, encased in dry ice. NCIS is called in.

Tony is at his desk, staring at his phone, waiting for a call. When it comes in, it turns out to be McGee playing around with him; Tony glares at McGee. Gibbs arrives. "Gear up!" and off they go to the Dry Ice Man.

Tony is taking pictures and being Typical Tony, is annoying one of the army guys at the same time. He also discretely takes a photo of the security access password for the building. Ducky and Palmer arrive on the scene (late as usual) and when they open Dry Ice Man's box Ducky and Gibbs reminisce about a past case before leaving. McGee arrives in a black van but instead of parking next to the NCIS truck and Ducky's ME van at the entrance to the facility...he pulls up unnoticed and parks around the corner. As McGee moves from the driver's seat to the back of the van, we see it's filled with surveillance equipment. Gibbs shows up a few seconds later and McGee uses the pictures Tony took of the password to hack into the facility's computers.

Later that night, outside the facility, Ziva and Tony emerge from the shadows and using the stolen password break into the building. Directed where to go by McGee who now has a map and video footage of the building - it's classic Mission Impossible, NCIS-style, complete with looping security tape showing all is well. Unfortunately, the looping tape eventually sets off an alarm. Ziva and DiNozzo make a run for it but guards appear from everywhere; they're trapped.

Scene change: Three Days Earlier.

Gibbs is pacing around as Palmer and Ducky talk shop, typical ME-speak. Palmer excuses himself "Ducky wanted privacy". He's then called up to Director Vance's office where he is told that the Secretary of the Navy wants to beef up security so they don't have anymore breaches, "like Agent Langer".

Scene change: Abby's lab.

Abby is busy working away when someone walks into her door. From the other side we hear McGee exclaim "Abby!" Abby quickly shuts down almost all of her computers while claiming that she's in the shower. She opens the door for McGee who is there to collect two boxes of evidence. McGee is curious as to what she's working on but Abby denies working on anything, however, she is quickly shutting down yet another computer when someone else walks into her door. We hear Tony call out: "Abby!" as he, too, walks into the locked door. He and McGee then proceed to the evidence garage with Abby closing the door behind them.

In the evidence garage are three chairs, a table and a whiteboard; McGee claims to have college flashbacks. Gibbs walks in and hands each of them identical files before writing "domino" on the board, then underlining it.

McGee starts to explain that it's a Navy thing but stumbles over his description, and Ziva finishes our lesson on "domino" (which is the US plan in response to an attack on Isreal). Gibbs tells McGee to study up on it, then tells the team that SecNav wants them to break into the highly guarded building we saw in the first chapter. He claims it's for a security test and adds that even the guards who are guarding the building don't know their security is about to be tested.

Scene change: The Bullpen.

Ziva, McGee and Tony are crowded around Tony's desk, eating a pizza, and discussing what would be the best way to break into the building. As they're discussing options Agent Lee comes up and tries to take a slice of pizza. Tony will only let her have a slice if she can come up with a way for them to "hypothetically" break into a top security facility. Agent Lee mentions "Ziva's brother", and Ziva is quick to correct her with "half-brother". The team remembers Ari's body bag strategy, and with it being a good idea Agent Lee is allowed a slice of pizza. As she reaches into the box, Tony tells her "small piece".

Back at the evidence garage, the team is telling Gibbs of their plan, with their emergency exit being a sewer line. They ask Gibbs if they should ask Ducky for a body, but Gibbs tells them to just take it. (Gibbs Rule #18: It's better to seek forgiveness than ask permission.) McGee suggests using a fire alarm because the doors would automatically open but Gibbs says it has to be discrete. He also tells them that nobody gets hurt in this "test".

Scene (& Time) Change: Present Time.

The alarm has gone off and Tony and Ziva are running. McGee's security feed fills with "snow", then the computers freeze and shut down. Tony and Ziva are ambushed by soldiers but instead of giving in quietly per Gibbs' orders Ziva fights back. Seeing this Tony backs up his team mate and the two go down fighting. As one of the guards hits Tony with the butt of his rifle, Ziva kicks a female soldier into a door, but there's too many guards and as they overwhelm her, the female soldier she kicked comes back and punches her in the face.

Ziva wakes up with a bloody nose. She's being interrogated (threatened?) by a stranger holding a cigar cutter (remind anyone of Darkman's opening scene between Durant and Black? Ouchx10). When Ziva demands to see Tony, the man tells her that she and Agent DiNozzo will soon be reunited again, and sure enough, Tony appears with quite the beat up face. Typical Tony is trying to make light of the situation, talking about playing poker and drinking, but Ziva cuts him off and asks who the man was. DiNozzo hands her a coin that says "75th Secretary of the Navy" on it. Oops.

Our brave heroes are soon freed and we next see Gibbs, Director Vance and the now identified Secretary of the Navy speaking in Vance's office. They talk and talk and talk some more, and finally conclude that while Tony and Ziva didn't set off an alarm, they still got caught, meaning there's still a security breach in NCIS.

Finally (once more for laughs) it's Palmer's turn to walk into Abby's door. "ABBY!!!" Palmer is trying to hide from Ducky who is after him because he lost the dead body which turned up at the crime scene (dry ice man). Ducky is not happy from being kept out of the loop and neither is DiNozzo. While Ducky sulks in front of Gibbs, DiNozzo goes one level up and starts badmouthing whoever formulated the whole plot of manipulating them, thinking that it was Director Vance. Gibbs surprises both of them by saying it was his idea from the beginning. Gibbs once again goes to Vance and this time they openly discuss about Agent Lee being the bad guy or gal, and how they can catch her along with her handler. Back at the bullpen, Agent Lee is once more trying to overhear information as the team discuss her involvement in the killing of Langer.

Director Vance then runs a security check on every operative in every department, including Abby, who was still hiding behind her locked door. Using a device to allegedly detect high levels of a substance that would have rubbed off on anyone associated with the Domino case, surprisingly it is Abby who comes under suspicion.

Abby is taken to the interrogation room, accompanied by McGee, who is extremely worried and concerned about her. McGee cannot understand how Abby could have been the traitor, considering it would mean losing her lab and losing Gibbs' trust - and she loves both more than that. Director Vance comes in before they have finalized as to who will interrogate her. Abby stops the play acting and reveals to McGee that she is not the traitor, far from it. In fact she has been working on the case from the very beginning (another example of Abby being truly Gibbs favourite?) McGee does not care...he's just overjoyed that Abby is not the traitor and jumps in to kiss her on the cheek.

Their plan works and the real traitor, Agent Lee, is suitably deceived. Director Vance tricks Lee into believing that she is above suspicion and despite the security lockdown, allows Lee to leave the building in search of a legal operative. Once she is outside, Lee goes to a designated paper stack (newspaper box in America) and makes a secret signal, all the while being watched by Vance through binoculars, who gives the green signal to Gibbs and the team; Agent Lee is picked up and brought back in to NCIS.

Lee claims that she is being blackmailed and forced to carry out her traitorous actions. She says her daughter has been kidnapped by them and shows Gibbs a picture of her daughter. Vance comes in and advises Gibbs that there is no mention of a dauaghter in her file, but there is mention of a sister.

The team is discussing how much trouble Lee is in, who despite being a traitor is now walking towards the elevator. All is revealed when Lee gets into her car and we see Gibbs hiding in the backseat.