Ve svém domě na vojenské základně je zavražděn námořník. Armáda posílá Gibbsovu týmu na pomoc plukovníka Hollis Mannovou, se kterou měl Gibbs milostný románek. Větším problémem je však to, že hlavní korunní svědkyní vraždy je Gibbsova bývalá žena...

In the squad room, Abby has spent her tax refund on IPods for each of the team. Ziva arrives listening to an Israeli song about a heroic woman who defies the mob to save a bad guy (lyrics in English here), Tony arrives singing 'Luck be a lady tonight' (loudly) and McGee is listening to instructions on how to be an alpha male (oh no McGee...it is too painful). Abby tries to explain to Gibbs how he can listen to 40000 songs on his player. He says he only listens to 5. ("5000?" "No. Five") Abby offers to give him her collection, of things like Android Lust, Flesh eating Foundation or Suicide Commando. Gibbs answers phone, yells "Dead Marine" and Abby says she's never heard of that one.

Lt Col Mann is already at the crime scene (we are not told how she managed to retire, hand over her command to someone else and now be back at work as if nothing had changed but if Gibbs can do it, others can too).
Mann is in charge. She asks Gibbs whether the team know that they are seeing each other - he looks vague. Tony gets confused as to how to address her. His antennae for Gibbs' private life is just going all crazy with signals.
Ducky sets a time-frame for the death and, since the deceased had been on his computer, they take his laptop. The boss from DIA insists that the secrets are too secret so he sends along his own computer person to keep an eye on Abby. She resists (memories of Chip, the lab rat who framed DiNozzo) but has no choice.

Major Sweigert is from the DIA His fingerprint is on the door to the Reynolds' house. His alibi is a date with Stephanie Flynn, the woman who was with Mrs Reynolds when she found the body. Stephanie is Gibbs' third ex-wife.

Mann takes Gibbs to see Jen to talk about Stephanie. Jen clarifies that Stephanie was his 2nd (Gibbs: 3rd!) ex-wife and they lived in Frankfurt (Gibbs: Moscow!) for two years (Gibbs: 1 year). And it won't be a problem because Mann will do the interrogation. Gibbs is making eye contact with no one if he can help it. Jen likes to see him squirm.

Mann interviews Stephanie and makes a Freudian slip asking how long Stephanie has known "Gibbs..er, Major Sweigert". Stephanie is "feisty". Tony and Ziva, in the observation room, discuss who is prettier, ex-wife number 3 or future ex-wife number 4. Tony says the army clothes make it hard to tell with Mann and Ziva instructs him to not picture her naked. Gibbs turns out to be standing behind them, in the dark- they cannot be sure how long he has been there. Tony and Ziva leave.
Stephanie, interrogated by Mann, insists on seeing Gibbs and yells for him. He arrives with coffee in hand for Stephanie, decaf as she likes it...and ordinary coffee for Mann. Mann lets Stephanie and Gibbs talk, semi-privately.

McGee interrupts to call him to Abby's lab. Stephanie is free to go.

In Abby's lab, Abby has bonded with the Human Computer Chip and found that Reynolds was doing email and into a file sharing application from which he got Tom Lehrer's "The Elements Song" that recites the periodic table to a tune that closely resembles 'I am the very model of a modern major general'. It was embedded in the computer and is a secret that Abby has to unravel: why was this song what he was sharing just before he died?

In Ducky's lab, Ducky is replying "That must have been extremely awkward for all concerned" to Mann. They discuss hearts. Ducky sees that they are really talking about Gibbs' heart, not the dead Marine's. So they discuss Gibbs. Mann doesn't want to be another Gibbs mistake since he has been married 3 times. Ducky reluctantly corrects her: 4 times. "Jethro's married?" "Heavens no". "Then how..? Oh!": she realises that he must be a widower. Mann realises that Kelly, that he named the boat after, is..?...and Ducky supplies the story. Mann's eyes film with tears. Gibbs arrives. Ducky explains the substance he found on the dead Marine's cheeks. Tears. He was crying when he died. Mann is looking very strained.

Tony and Ziva arrive in autopsy: Capt Reynolds' phone discloses nothing but Major Sweigert had been talking to Capt Reynolds' wife. The wife was having an affair with Sweigert. Her alibi is a conference in Charlottesville, a 2 hour drive away so she could have done it. She has insurance reasons to not want a divorce, so they get a warrant for her arrest.

Stenography is Abby's latest good idea in the lab, to hunt down the hidden file in files with the elements song. The Human Computer Chip offers more help. She resists: she is a control freak. But he is charming her more and more. Mann and Gibbs enter the lift. Gibbs stops it and asks what's wrong. She asks "how long have we been together"...Gibbs just turns on the lift again. Mann flicks the lift to stop. So they stop start stop until Mann confronts Gibbs with not telling about Shannon and Kelly. He says "They're dead. End of story. I've put it behind me". Mann asks "Have you?" He flicks the switch to restart the lift. End of conversation.

McGee tries to persuade Gibbs to let him go work with Abby and Human Computer Chip in Abby's lab. Gibbs stares him into changing his mind and sticking to finding Mrs Reynolds on ATM cameras in Charlottesville. Gibbs leaves. McGee vents at Mann about women needing to see through surface charm. Mann, mind on Gibbs, agrees.

Tony and Ziva catch a DIA officer at the Reynolds house as they go to arrest Mrs Reynolds. He reveals the death benefits payments she will get. She is obsessively cleaning the house. It is completely wiped. "Cleaning is kind of therapeutic for me".

McGee goes to the lab and hears Abby saying "Give it to me baby, don't make me beg" but, of course, when he looks, she is talking to her computer. He brings Caf-Pow. Abby and the HCC already have one each. McGee gives a good idea. Abby hugs HCC as if it was his idea. Abby leaves. McGee and HCC have a Caf-Pow showdown.

Stephanie is seeing Jen and asking for Gibbs to be taken off the case. Stephanie gives a look: Jen asks if she learned the look off Jethro. Stephanie wants to protect Sweigert from career harm. She asks whether Jen and Gibbs had something together: Jen says "only professional".

Jen brings Stephanie to the squad room to see Gibbs and Mann and reassure Stephanie that Gibbs won't hurt her or her boyfriend. Mann says she will monitor Gibbs closely. Gibbs gives the look. The women each comment on it.

In interrogation, Mann confronts Mrs Reynolds over her affair with Sweigert. They tell her Reynolds was reading the love-emails and crying when he died. She shows distress. She denies killing him. Gibbs and Mann get called to the lab: McGee has found ATM footage of Mrs Reynolds at the conference in Charlottesville so she has an alibi. She really does clean for therapy.

There is a one-point print that has yielded 80,000 hits on the AFIS database. Mann wants to bring in Stephanie as she might have known of the affair and have motive. Gibbs says wait. They dispute. Tony notes to Ziva from the sidelines "This never turns out well for the kids". Mann asks what if Stephanie did it. Gibbs says "She'd walk". and then "You don't know Stephanie". He invites Tony to call Stephanie and invite her in. Turns out she has left her job.

In Abby's lab, she is getting closer to the secret on the computer in the elements song. HCC notes that Abby's cleverness is intimidating. She works out that the element song can be filtered. You get a handful of the elements audible. Each has a number on the periodic table, so the names of the elements converts into a numeric code, but what does the code mean? HCC answers her phone and tells her that her boss wants her. She secures the laptop in an evidence bag and leaves HCC in the lab to go see Gibbs. Gibbs did not call her. She has left the HCC in lab with the evidence. McGee announces that the mystery fingerprint 80000 includes the HCC. He is another lab ratfink! They race back to lab, leaving McGee to unravel the meaning of the numbers from the elements song. The computers are wiped. They all realise they are looking at the killer but have no proof. He walks out, trailed by the team. They slow him down. Abby keeps asking can she hit the HCC. Gibbs says no each time.

McGee, in the nick of time, discovers that the numbers are the bank account for money from the sale of defence secrets. Reynolds and HCC took a million from a Beirut source. "What did you sell and who did you sell it to?" Ratfink: "Maybe if you cut me a deal, I'll tell you." They have him. Abby is now permitted to hit him. She does. On the nose.

Mann and Gibbs, well dressed in party clothes and Gibbs carrying an ice bucket with beers, are cheerfully descending into Gibbs' dimly lit basement, with Mann asking why all romantic nights on the town finish with sanding boats in the basement. Turns out Stephanie is sitting inside the upturned boat. Embarrassed, she stands, rubs her hands over the "Kelly" name on the boat and comments "Sweet", with a smile. She hands back dog tags to Gibbs (she found them 6 years ago). She is not staying. (She wishes Mann "good luck", nicely, as she leaves.) Gibbs walks her out to her car (we see he lives in a street with a view of the Capitol Building at the end of it.). She says why she quit her job: go back to her family in Philly as she knows of Sweigert's affair. She wonders why, when she was mean about him, Gibbs didn't throw it in her face: he says he wouldn't do that to her.

She laments that it never works out for her. He hugs her and says "Me. Us. It's not your fault". She says "It wasn't anyone's fault". As she's about to drive off, she smiles, weakly, and says "but we'll always have Moscow" . Gibbs gives his half-grin and nods. He seems cheered that they have parted amicably. He's feeling pretty good tonight: case solved, ex-wife is OK with him and Hollis is waiting, looking gorgeous, in the basement with his boat and a beer.

Meanwhile, in the basement, Mann has found a cassette player with empty cassette cover on his workbench. She, too, is perky and mutters to herself: "Jethro, you never cease to surprise me. Music!" and she hits 'play'. And the music comes: solo piano, very simple, naive, like early Mozart . Mann is smiling, glancing back at the cassette and shaking her head slightly at Gibbs' odd taste in music as she takes off her jacket and starts with the sandpaper. But then the music stops and it's now happy voices: Kelly's voice. Mann's smile fades. Kelly and Shannon crowing that Kelly won second place in the piano competition and when "you come home Daddy, I'll be really good at it". By this time, we see Gibbs has stopped midway down the stairs, sitting, staring straight ahead, listening. Mann puts down the sandpaper and walks over to the cassette player, staring down at it, wide-eyed. He catches his breath and lets it out, listening as the tape continues with 'come home soon' and 'love you' and 'we miss you' messages and Kelly's kiss for daddy. The voices cease. Mann lifts her chin and swallows hard, looking straight ahead. He exhales and then turns his head towards Mann. She turns her head and looks at him. Mann's eyes are filmed with tears. He doesn't take his eyes off her.