NCIS: Los Angeles will lob a curve ball early in season 7.

'NCIS: LA' Season 7: Premiere Title Announced, Will Tony DiNozzo Really Feature?

The cast is currently filming for episode 702 (airing order unconfirmed), and the Dave Kalstein penned script is already being billed as a major game changer. Although NCIS: LA skipped out on a season finale life or death cliffhanger last spring, the anticipation building around "Citadel" could rival the usually agonizing summer hiatus.

"Game-changing episode of NCISLA starts production tomorrow! See you on set @ 6:30 AM... #citadel," Kalstein tweeted on Monday night. The scribe than followed up with a photo from set early Tuesday morning.

'NCIS: LA' Season 7: Deeks Takes A Tumble [PHOTOS], Is Kensi To Blame?

Little can be deduced from the photo, however. While it is always nice to see Sam (LL Cool J), what fans are really hoping for is a glimpse at the new mystery character previously teased by production manager Rick Tunell. "Citidel" is primed to introduce a highly anticipated character - one that fans have been dying to see - and we're itching to find out who this secret guest star will be.

The photo does raise one question, however. How many episodes has Sam worn that red shirt in? All of them?

Catch Sam and his indestructible shirt when NCIS: LA returns to CBS on Sept. 21 at 10 p.m. ET. Click the video below to see a teaser for the season 6 finale.

Tags: NCIS: LA NCIS: Los Angeles television CBS