The Real Reason Mark Harmon's Gibbs Didn't Return On NCIS Season 21's Ducky Episode

"NCIS" fans experienced one of the toughest episodes to watch of the long-running series with Season 21, Episode 2 — "The Stories We Leave Behind." The episode addresses the death of Dr. Donald "Ducky" Mallard, mirroring the real-life passing of the character's actor, David McCallum, last year. The episode begins with the discovery that Ducky died in his sleep, with the rest of the storyline being a tribute to both the character and McCallum himself. While there is a special guest star in the form of Michael Weatherly returning as Tony DiNozzo, one former "NCIS" mainstay was conspicuously absent.

Mark Harmon did not return to play Leroy Jethro Gibbs in a move that upset some "NCIS" fans. Brian Dietzen, who plays Jimmy Palmer on the series, addressed Gibbs' absence. Apparently, there was talk of getting him involved, but it didn't come to fruition due to "a scheduling conflict." Dietzen told The Wrap, "I think everyone would love to see Gibbs make an appearance at some point. That is such a beloved character, TV history." 

While Gibbs not coming back to pay respects to his long-time colleague may be disappointing to some, Dietzen was happy with what the episode accomplished. Dietzen's Jimmy even gets to share a scene with Tony in a moment that surely pulled at plenty of people's heartstrings. The actor continued, "I'm really happy with the way [the scene] turned out. The way that it works with Jimmy and Tony. There's an intimacy to that and there's a familiarity to that."

To honor the legacy of Ducky and McCallum, "The Stories We Leave Behind" utilizes clips from old episodes featuring McCallum, including an instance where he speaks with Mark Harmon's Gibbs. In that way, the tribute does manage to incorporate Gibbs, even if it wasn't in the way a lot of fans had hoped. But putting together any episode of television is a massive undertaking, and Brian Dietzen elaborated on the many ideas they circulated through before winding up with what fans saw. 

Dietzen told The Wrap, "Every idea under the sun was thrown out [for this episode.] From having every 'NCIS' cast member from every spin-off come together in a huge funeral theme... nothing was off the table." However, he then mentioned that there are always logistical things with these kinds of moves. People on various "NCIS" spin-offs undoubtedly have their own schedules, likely filming at the same time the main series was. And Mark Harmon could have any number of things going on that prevented him from swinging by for a quick appearance. 

Gibbs not being around for Ducky's tribute episode may not be all too surprising, given what Harmon has said about a potential return. In November 2023, Harmon spoke with Entertainment Tonight about what he thinks Gibbs is up to these days: "He's probably sitting in a stream up in Alaska fishing. Is he going to get out of the stream? I don't know. But if he is, I don't know about it." And who knows? Maybe Gibbs could return in another "NCIS" episode down the road and pay his respects to Ducky then.