NCIS season 18 will be airing its 400th episode once it premieres later this year on CBS. It's yet to be seen who could be appearing in this particular episode. But, the good thing is that it seems like the casting process is underway.

In a recent Twitter post, Brian Dietzen (who plays Dr. Jimmy Palmer) shared a message from casting director Jason Kennedy. He indicated that they are finding the right performers for this specific episode airing in NCIS season 18.

Usually, the casting process takes place before filming an episode to guarantee the availability of the people involved. The 400th episode is an origin story for Leroy Jethro Gibbs (plays by Mark Harmon) and Dr. Donald "Ducky" Mallard (David McCallum).

We could see some flashbacks in NCIS season 18, possibly showing the early days of the two working together. The younger versions of Gibbs and Ducky might be shown, wherein they're taking certain cases in the past. The casting might be linked to what's needed to be done and some new faces could appear.

Gibbs and Ducky's history is the center of everything in the 400th episode. We could learn more about their origins and the things they've been through in the past. Their relationship evolved compared to where they started back in season 1.

Meanwhile, NCIS season 18 is, reportedly, slated to resume filming after the Labor Day Weekend. Once production is underway, we could expect more updates about what's coming and some guest stars set to appear. Despite the uncertainties, the upcoming installment is said to be premiering in November.

Although the plan is tentative and could be changed, some speculated the new season will be released in the said month. If CBS proceeds with this plan, we could expect the series to return on Tuesday, Nov. 10. It could have enough time to prepare everything if filming begins in the second week of September.

The series starts filming mid-July leading to a late September premiere. But, due to the current global health crisis, the show wasn't able to follow that particular schedule. In the event the upcoming installment premieres in November, we could expect three episodes in that month.

After that, the series will release two or three episodes in December before cast and crew go on a holiday break. Yet, CarterMatt noted that NCIS season 18 could have shorter hiatus this time around to make up for the lost time by filming over the holiday.