The series stars Mark Harmon, Sean Murray, Wilmer Valderrama, Katrina Law, Brian Dietzen, Diona Reasonover, David McCallum, Rocky Carroll, and Gary Cole.

Harmon departed the series as a regular after the fourth episode, "Great Wide Open" but still appears in the title sequence for the remainder of the season.

McGee, Torres, and Knight apprehend a man believed to be tied to the killer, but soon discover he is undercover FBI agent Alden Parker (Gary Cole) who was also investigating LeMere.

When Knight mentions the name of the account paying him in interrogation, LeMere shoves the desk at her, breaking the glass and allowing him to escape and hold Kasie hostage in the squad room.

An FBI team led by Parker has a warrant for Gibbs' arrest due to his actions in the case against LeMere, but find his house deserted with a large hole in the basement (finally answering the series-long question of how he gets his boats out).

Gibbs decides to stay in Naktok Bay, feeling a sense of peace he hadn't felt since the deaths of his wife and daughter, and bids an emotional farewell to McGee.

The team investigates the death of a soldier believed to be linked to a suicide bomber, only for the body to explode before Jimmy can examine it, prompting Ducky to once again suit up in scrubs.

While Tobias Fornell (Joe Spano) and Dr. Grace Confalone (Laura San Giacomo) assist NCIS in the apparent suicide case of a Naval officer in Palmer and Knight's grief group, Torres is informed by old colleague and friend Jane Tennant (Vanessa Lachey) that a witness in an old case of his has resurfaced, but when they pick him up, their car is hit by a barrage of gunfire and overturns.

Vivian assists Torres and Knight by telling them her memories of where she was held captive, and the agents find the location empty but "nevermore" is written on the wall, meaning the Raven is back with a vengeance.

Showrunners of both series had previously mentioned crossing over and CBS Entertainment President Kelly Kahl had stated that discussion about a crossover would start after NCIS: Hawaiʻi finished its first batch of episodes.

[26] On April 29, 2022, it was reported that Jason Antoon would be appearing in the nineteenth episode of the season as his NCIS: Hawaiʻi character, Ernie Malik.

[29][41] On October 11, 2021, it was officially announced that Harmon would be departing the series, with the fourth episode, "Great Wide Open", being his last appearance as a regular.