Behind the Scenes of the 'Frightening' 'NCIS' Season Finale

This video is unavailable because we were unable to load a message from our sponsors.

If you are using ad-blocking software, please disable it and reload the page.

No one is safe on tonight's season finale of NCIS!

"We're going into a very disturbing territory on NCIS at the end," Pauley Perrette tells ET. "What's happening here is really going to stick with people. It's a terrifying thing."

NEWS: Why NCIS is the No. 1 Show in the World

In the finale, titled "Neverland," the NCIS crew ardently investigates a global terrorist group recruiting teens via the Internet after a deadly bombing overseas results in an emotional and surprising loss for the team.

While the tone of the show is serious, the mood on set stays lighthearted, which makes for some great behind-the-scenes footage.

"We always have an outstanding NCIS gag reel, which no one gets to see but us," Pauley said. "If there is a gag reel, 20 minutes of it is Michael Weatherly."

NEWS: NCIS Star Michael Weatherly Reveals 35-Pound Weight Loss

Watch the video to see Michael in rare form, goofing off on set.

NCIS airs Tuesdays at 8 p.m. ET/PT on CBS.

Related Gallery