Though producers prefer you didn't call Tuesday's episode a finale, NCIS finished Season 17 with a powerfully poignant performance from Christopher Lloyd that honored war veterans' valor and sacrifice.

"The Arizona," which had Lloyd playing World War II veteran Joe Smith, toyed with viewers' perception. At the start of the episode, Joe had broken into a military family's home and stolen a Purple Heart. Ultimately, he wanted to have his remains on the U.S.S. Arizona, as a means of honoring his service during the attack on Pearl Harbor in 1941. But the key question Torres (Wilmer Valderrama), Vance (Rocky Carroll), and Gibbs (Mark Harmon) faced was: Is Joe telling the truth?

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Mark Harmon and Christopher Lloyd, NCISMark Harmon and Christopher Lloyd, NCIS

Lloyd, beloved for his timeless turn in Back To The Future, was positively electric as the veteran, equal parts outraged at the lack of awareness about the attack on Pearl Harbor and seemingly disoriented at times, too. His role required a tricky balancing act that had him appear both convincing and suspicious, as all through the episode clues mounted that he was telling the truth or not telling the truth in equal measure. Nearly everyone on the team doubted his story, except Gibbs — pretty much the lone officer willing to give Smith the benefit of the doubt.

In the end, it turned out that Smith had indeed been on the vessel, and deserving of the military honor he had been demanding. By the story's conclusion, Gibbs had not only been vindicated but also changed; the experience caused him to dig deep into his own feelings about his sacrifice, and expose some vulnerabilities he'd otherwise keep tucked away. In a conversation with TV Guide, Gina Monreal, a co-executive producer on NCIS and a writer of the episode said she had long wanted to do an episode that brought the events of Pearl Harbor back into public consciousness.

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"I've always wanted to do this, and right now it's imperative," she said. "People who served in World War II are in their 90s and 100s and pretty soon they're not going to be around to tell their stories."

The story was partially inspired by her grandfather-in-law, who served in the war; she said he never wanted to talk about his experience until close to his death. Before he died, he talked about liberation of a concentration camp. The National World War II Museum says that 294 WWII veterans die every day, "It made me realize how many more stories out there needed to be told. We were on a ticking clock to get this episode made and get this story out there."

She's grateful for the episode not just because it tells an important story, but also because she got to get the ideal actor for the guest role too. "[Christopher Lloyd] was the person I had in mind writing it," she said. "His voice was in my head, and when he came on board it was a complete thrill — a highlight of my career. It was a dream come true."

Gibbs was changed after the experience, feeling a deep personal connection to Smith because his father was a WWII veteran as well. The usually stoic Gibbs opened up to McGee about his past, seeing the ramifications of the sacrifice he's made for the team and his family, and fans can expect to see Gibbs opening up more as NCIS continues.

"In this episode, the journey he takes with Joe, seeing what it did for Joe," Monreal explained. "Gibbs ended up being inspired by his story and McGee was the perfect choice for him to open up to, like a son."

"The Arizona marked a turning point in Gibbs' growth, Monreal continued, and she said the potency of the storyline is in large part because of Mark Harmon's abilities as an actor and producer. "He's able to inch the character forward in powerful ways. After 17 years, he still does things that surprise us."

Mark Harmon and Christopher Lloyd, NCISMark Harmon and Christopher Lloyd, NCIS

NCIS is on hiatus until Season 18; past episodes are on CBS All Access.