With millions tuning in to CBS’ long-running military crime drama “NCIS” over its 21 years on air, it’s likely you’re familiar with Leroy Jethro Gibbs.

Yes, the tough-as-nails team leader played by Mark Harmon in more than 400 episodes, known for his intense stares, strong personal ethics, and concise speech?

Did you realize that Gibbs’ backstory extends even beyond his two decades on television?

This is what CBS aims to explore with “NCIS: Origins” (Mondays, 9 EDT/PDT; shifts to 10 PDT/EDT on Oct. 21, ★★½ out of four). Set in 1991, the series stars Austin Stowell as a younger Gibbs, taking over the role from Harmon’s son Sean, who previously portrayed young Gibbs in flashbacks on “NCIS.” “Origins” blends patriotism, military life, and weekly murder mysteries, while enhancing the experience with a stellar period soundtrack that surely cost a pretty penny in licensing, further wrapped in a neo-noir aesthetic fitting for a grieving Gibbs, whose family has just been tragically killed.

Similar to previous “NCIS” series set in Los Angeles, New Orleans, and Hawaii, “Origins” fits neatly into the established procedural format of the original, even if it leans a bit too seriously at times. The lead character, however, feels like one of the less engaging aspects of the show. Still, the writers construct intriguing cases for each episode, and the cast is recognizable and relatable. If you’re looking for more of the same but with a slight twist, CBS has delivered once again.

In this new series, the young Marine Corps Scout sniper-turned-special-agent Gibbs arrives for his first day at the San Diego NIS office with bruised knuckles. (For context, the federal agency was once called the “Naval Investigative Service.”) As the rookie officer, he earns the nickname “probie” while learning to gather evidence and trust his instincts. While he copes with his family’s tragic loss, he also works to bring criminals involved with the Navy or Marine Corps to justice, which, as always in the “NCIS” realm, seems to be a highly frequent occurrence.

Stowell, who is relatively unknown except for some TV appearances and his leading role in the romantic comedy “The Hating Game,” clearly studied Harmon’s performance in “NCIS.” He embodies Gibbs’ trademark stoicism and brusque nature with ease. His intense glares and striking jawline certainly make him a fitting choice for the role. However, if his portrayal of Gibbs feels both inscrutable and underdeveloped, it highlights a core challenge in building a show around a character often perceived as enigmatically mysterious.

If Gibbs is the least compelling aspect of his own backstory, that’s not a major issue. The creative team for “Origins,” including series creators Gina Lucita Monreal and David J. North, knows how to assemble a charming group of Navy investigators in their caps and gloves, now marked with “NIS” instead of “NCIS.”

The cast features Lala (Mariel Molino), a capable and driven woman who questions Gibbs’ mental health while proving to be an exceptional investigator herself (think Ziva from the original series). There’s Randy (Caleb Foote), who brings an earnestness reminiscent of McGee alongside a quirky nickname. Secretary Mary Jo (Tyla Abercrumbie) assumes the role of the nurturing figure. Plus, fans will enjoy seeing younger versions of familiar characters: agents Mike Franks (Kyle Schmid) and Vera Strickland (Diany Rodriguez), who contribute to the nostalgic element. As Gibbs’ boss, Franks attempts to keep the impulsive newcomer in check, but he’s not overly concerned—he has his own disregard for the rules as well.

Though some clichés are prevalent and the plotlines can be overly dramatic, “Origins” strives to elevate itself as a more thoughtful version of “NCIS.” Lala navigates the challenges of Franks’ obvious sexism and office dynamics. Meanwhile, Gibbs grapples with serious trauma that he has yet to process, and Franks is burdened by guilt over a failure in Gibbs’ family case. While the series may not produce profound moments, it does aim to delve into themes that are more mature compared to its predecessors, which are often known for melodramatic twists and simplistic moral dichotomies. It earns points for its aspiration to grow beyond its origins.

Enjoy watching the charming Harmon Stowell and his team tackle naval crimes in the ’90s. Appreciate the sometimes cheesy dialogue, accompanied by former “SNL” star Bobby Moynihan as a forensics technician. It’s familiar yet refreshingly new.

If this latest “NCIS” spinoff doesn’t grab your attention, don’t worry—there will be more to come.