Go back in time as a young Leroy Jethro Gibbs begins his career as a newly minted special agent in the new CBS series "NCIS: Origins."

The origin story of Leroy Jethro Gibbs has finally begun: CBS kicked off its much-anticipated prequel Monday from veteran NCIS writers-producers Gina Lucita Monreal and David J. North, as well as CBS Studios. And as promised, Mark Harmon returned to both narrate and to appear fireside as he journals about his life.

"NCIS: Origins" may not stray far from the DNA of its flagship, but the updates to the formula make revisiting Leroy Jethro Gibbs' past a "darker" chapter for the beloved CBS franchise. The new series turns the clock back to 1991,