Agent Farnel is with his daughter, at one of her friend's birthday party's or something, when this escaped criminal (ex-petty officer) comes in and practically threatens him. He says that he is innocent and that he wants Farnel to reopen his case. Farnel can't do anything in front of his daughter. Long story short, Farnel has Director Shepherd jerk Gibbs out of retirement.
Meanwhile, McGee it talking through his teeth. Tony demands to know why. Ziva won't say, so he turns to his probie, Lee. McGee accidentally bleached his teeth. Then they see Gibbs, who is going upstairs to complain to the director. When he comes downstairs, Lee is trying to figure out what to do (Tony has Gibbs' desk, McGee has Tony's desk and Lee has McGee's desk). Gibbs practically ignores them and goes to a completely different place.
Tony: Ok, maybe he lost his memory again and forgot he quit his job.
Ziva: Wouldn't he be sitting at his OLD desk then?
Gibbs goes downstairs to Abby's lab with some Caf-POW. He asks her something and then Abby looks up a throw an enthusiastic mini party. Then Gibbs tells her that she is only here temporally. Abby is not happy (and that's putting it lightly). Gibbs asks her she can find something.
Abby: Anything… temporally reinstated Agent Gibbs.
Later, when Lee says that NCIS is much better off without Gibbs.
Abby: You do realize…
Lee: …that you can kill me without leaving forensic evidence behind? Yes.
Soon, the case is getting more complicated and Gibbs is getting more and more frustrated as he is missing Happy Hour in a canteena in New Mexico. He goes into the elevator, starts going to the lobby when the elevator starts going to a different floor… Abby's lab.
Abby is calling security, telling them not to let Gibbs leave the building. When Gibbs comes into her lab, Abby runs to him… then handcuffs his wrist to her own. Gibbs asks her to find out why the escapee knows every step the team is doing.
In the office, Tony is also getting frustrated. Gibbs comes in (un-handcuffed) and grabs Tony's phone… then pries it open with a knife. A bug.
I won't go into details, but they find the real convict… a guy who was trying to prove him innocent. He killed three guys and robbed a bank. Bought some pretty nice stuff as well.
Tony and his team are happily going back to the office. Ziva is saying that McGee sitting at Tony's desk is effecting him (McGee just used a DiNozzo move and got a date). Then they stop. McGee's desk (Tony's desk) is piled with Tony's stuff. Lee's desk is pretty empty… and Gibbs is sitting at his rightful place. With a mustache no less.