"McGee is kind of reflecting on the past and on the rules that Gibbs has tried to instill in the team over the years, and questioning some of those rules and just thinking back," Murray tells TVGuide.com. "He's going to spend the holiday with ... his dad, and that's something that he doesn't frequently do. They have a strained relationship. He's sort of estranged from his father, and part of him writing that letter, I think, is him getting out a lot of stuff he can't necessarily say."
The episode also calls back to the season premiere, as McGee takes the lead on a cyber terrorism case, and the team recruits previously seen villains to help them solve the case in the week before Christmas.
As part of McGee's nostalgia-fest, viewers will be treated to a host of flashbacks featuring current and former characters — including, yes, Ziva David (Cote de Pablo). "It's an episode that really, I think, is kind of a reward to longtime fans," Murray says.
Check out a sneak peek below:
NCIS airs Tuesdays at 8/7c on CBS.
(Full disclosure: TVGuide.com is owned by CBS.)