The long-running NCIS is doing something for the first time in the upcoming Season 20: starting a new season without Mark Harmon's Agent Gibbs. While the hit series did find the perfect replacement for Gibbs after Harmon left mid-Season 19, it's still a big deal to be starting a whole new season without him. As sad as that is, NCIS won't have anything to worry about because it will begin Season 20 with a time-honored NCIS tradition.

After 19 seasons, it's hard not to repeat common plot threads. NCIS fans know that having an agent run from the law has happened a few times, and given Gibbs' penchant for breaking rules, that shouldn't be a surprise. However, Gibbs' team members were always ready to risk everything to get him out of whatever tight spot he found himself in. That's exactly what's going on when Season 20 picks up -- except there's no Gibbs. Here's how the iconic agent's absence will set the tone for the new season.

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After some early rough patches, Gary Cole's character Alden Parker spent Season 19 settling in nicely. Some of his best traits included bird-watching, a love for pastries and a working knowledge of technology (the latter possibly a dig at Gibbs). However, the team didn't know much about Parker's past until the season finale. His ex-wife Vivian Kolchak reached out to Parker for help, but then Parker's former FBI partner turned up dead with Parker's DNA on the body. Clearly someone was framing him for murder, and on top of that, the FBI was also investigating Parker for fraud.

Knowing that the FBI was out to get him, Parker decided that he was going to turn himself in. He even told his team, "I'm not Gibbs. You don’t owe me anything." At first, the team agreed, but after some prodding by Ducky, they decided that they wouldn't let Parker give up. He had been there for them several times throughout Season 19, and it was time for them to do the same. When Parker asked why they were so insistent on helping, McGee told him, "Because you forgot Rules 5, 8 and 15."

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Understandably, Parker was confused, but those numbers were obviously referencing Gibbs' rules. Rule 5 is "You don’t waste good," while Rule 8 says "Never take anything for granted," and Rule 18 states "It’s better to seek forgiveness than ask permission." McGee said they would make a list for Parker -- which is something that Gibbs never did. Even though the character is no longer on the series, NCIS is making sure to honor his legacy through the continued use of his fan-favorite rules.

The rules provide an easy way to reference Gibbs on a regular basis. More importantly, though, it matters that McGee and company were sticking up for Parker. It might be a time-honored tradition for someone to be running from the law, but the fact that the team was willing to risk everything to help Parker just like they did for Gibbs means that they are starting to see him as family, not just a boss. While Gibbs may not make an in-person appearance in NCIS Season 20, his spirit lives on through the actions of his team members.

NCIS Season 20 premieres Sept. 19 on CBS.