'NCIS' Episode 400: Gibbs & Ducky Meet in Flashbacks (PHOTOS)

Mark Harmon David McCallum NCIS Episode 400 Gibbs Ducky
Sonja Flemming/CBS

NCIS has reached another milestone — its 400th episode! — and the November 24 episode is going way back in the history of two of its original characters: Special Agent Leroy Jethro Gibbs (Mark Harmon) and former medical examiner, current historian Dr. Donald "Ducky" Mallard (David McCallum).

In "Everything Starts Somewhere," flashbacks will show the murder case that introduced a young Gibbs (played by Sean Harmon, Mark's son) to NCIS, then NIS (he won't join for some time) and young, new-to-America Ducky (played by Adam Campbell).

'NCIS' Episode 400 Digs Into Ducky & Gibbs' BackstorySee Also

'NCIS' Episode 400 Digs Into Ducky & Gibbs' Backstory

Plus, executive producers Steven Binder and Frank Cardea give some insight into Gibbs' flashback mission.

Both characters "are at crossroads in their lives," executive producer Frank Cardea previously told TV Insider. "They [will] help each other find their life paths."

Scroll down for a look at Gibbs and Ducky, both past and present, in Episode 400.

NCIS, Tuesdays, 8/7c, CBS

Vito D'Ambrosio Mark Harmon NCIS Episode 400 Jonny Zucado Gibbs
Sonja Flemming/CBS

How long will it take for Gibbs (Mark Harmon) to get Jonny Zucado (guest star Vito D’Ambrosio) to talk?

Maria Bello NCIS Episode 400 Jack Sloane
Sonja Flemming/CBS

Jack (Maria Bello)

Emily Wickersham Wilmer Valderrama NCIS Episode 400 Bishop Torres
Sonja Flemming/CBS

Bishop (Emily Wickersham) and Torres (Wilmer Valderrama)

Rocky Carroll Mark Harmon NCIS Episode 400 Vance Gibbs
Sonja Flemming/CBS

Vance (Rocky Carroll) and Gibbs

David McCallum Mark Harmon NCIS Episode 400 Ducky Gibbs
Sonja Flemming/CBS

Who’s in the photo?

Ducky Gibbs Kasie Lab NCIS Episode 400
Sonja Flemming/CBS

What has Kasie (Diona Reasonover) found?

Diona Reasonover Mark Harmon NCIS Episode 400 Kasie Gibbs
Sonja Flemming/CBS

Kasie and Gibbs

David McCallum NCIS Episode 400 Donald Ducky Mallard
Sonja Flemming/CBS

Ducky (David McCallum)

Gibbs Ducky Young Flashbacks NCIS Episode 400
CBS

Young Gibbs (Sean Harmon) and Ducky (Adam Campbell)

Young Ducky Gibbs NCIS Episode 400 Adam Campbell Sean Harmon
CBS

Young Ducky and Gibbs

Adam Campbell Sean Harmon NCIS Episode 400 Young Ducky Gibbs Office
CBS

Everyone knows a paint job is coming for those walls.

Sean Harmon NCIS Episode 400 Young Gibbs
CBS

Young Gibbs

Adam Campbell NCIS Episode 400 Young Ducky
CBS

Young Ducky