"NCIS" season 18 is almost here after a long hiatus with milestone episode. The second instalment of the season marks the 400th episode of NBC's long-running series starring Mark Harmon as Leroy Jethro Gibbs, Sean Murray as Timothy McGee, Maria Bello as Jack Sloane, and others. Here are a few spoilers for "NCIS" season 18 episode 2. Read on to find out what happens next.

[Spoiler alert! This article contains spoilers for "NCIS" Season 18. Do not read further if you don't wish to know more about it.]

The second episode of the eighteenth season of "NCIS" is titled "Everything Starts Somewhere" and will go back in time to visit the young Gibbs when he has just started his career. Fans are in for a full dramatic ride when the young Gibbs meets the young Ducky. Together, they will unravel the mystery of an old murder case.

"Flashbacks reveal the murder case that first introduced young Gibbs to NCIS and his introduction to young, new-to-America Ducky," reads the official synopsis for the 400th episode of the series as on Cartermatt.

Sean Harmon and Adam Campbell will return to play the role of young Gibbs and Ducky. Speaking to TV Line, executive producers Frank Cardea and Steven Binder revealed more details about the upcoming segment.

Written by Binder, this episode tells the story of the time when the two partners meet for the very first time. At this moment, they are at the crossroads in their lives and their acts lead them to where they are currently.

" Well, the story revolves around their first meeting and they're at a crossroads in their lives, each of them. I won't go into the exact nature of the crossroads, but it's a very pivotal moment in both of their lives and they're able to help each other get on the path that leads them to where we find them in the present day," Binder said of the episode.

The promo for the highly-anticipated episode is yet to be released. It is expected to be out after the broadcast of "NCIS" season 18 premiere this Tuesday.

"NCIS" season 18 episode 2 (400th episode) airs on Nov. 24 at 8:00 pm ET on NBC.

Mark Harmon
Mark Harmon as Leroy Jethro Gibbs in NCIS series CBS