NCIS is in full swing for Season 18 in hopes of getting the show on the air ASAP. November seems to be the date for having Gibbs (Mark Harmon) and the gang back on our TV screens  — a target that's of course in flux due in part to the ongoing COVID-19 crisis. When NCIS returns, fans can look forward to catching up on a number of important storylines, including how exactly Sloane (Maria Bellowill leave the show and what's up with the time jump backward to last year

But there's another big event happening: the show's 400th episode. It's not uncommon for reality shows, variety shows, or news programs to hit such a high episode count — Dancing with the Stars and Saturday Night Live for example, have aired over 400 and almost 900 episodes respectively — but for a scripted, live-action program, few shows of the modern era reach such an advanced milestone. (Law & Order is one; it aired 456 episodes in its 20 year run.) NCIS, which began in 2003, may well be on its way to matching that record if it pushes on a few more years, but for now, it's still got a big, respectable birthday coming up. 

NCIS of course ended Season 17 prematurely in April, two episodes shy of its quadricentennial with "The Arizona," the moving episode starring Christopher Lloyd as World War II veteran Joe Smith. When NCIS returns, it won't continue that storyline explicitly but will continue to explore the ramifications of it — especially with regard to how Gibbs has become more introspective and emotional. How will all that ladder up to NCIS's big anniversary episode? Here's what we know so far. 

Production has already wrapped 
According to a snap shared on Wilmer Valderrama's Instagram page, the team has already filmed the milestone episode — and apparently got some cool shirts to commemorate the special day, too. 

It'll be a flashback. "It's about how Gibbs and Ducky met," showrunner Frank Cardea told TV Guide in April. "It's a case that brings them back. There are wonderful moments and we see how Ducky and Gibbs met under strange circumstances."

Mark Harmon, David McCallum, NCISMark Harmon, David McCallum, NCIS

It may give insight into a mystery. The recent news that NCIS's opening episodes will dig into what happened when Gibbs went off the grid in the Season 17 episode "Musical Chairs" likely means we'll uncover more about Gibbs past. 

There may be some new faces or characters to emerge. Jason Kennedy, casting director on the show, posted a pic in August of a piece of paper with "NCIS #400" written on it — a clear indication the series is picking new peeps to populate the episode. Of course, these could be minor characters as much as they could be integral storyline folks, so we'll have to wait to see exactly what that means. 

PHOTOSEvery Major NCIS Guest Star Ever

Jamie Lee Curtis, Michelle Obama, Bob NewhartJamie Lee Curtis, Michelle Obama, Bob Newhart

NCIS aired its last episode of Season 17 before a hiatus on April 14. Past episodes are streaming on CBS All Access.