The stakes of the mole investigation on NCIS: Los Angeles just got a lot higher.

On Sunday's episode, the NCIS agents found themselves getting picked off one by one. No, not killed (well, not yet, anyway), but rather arrested. Deeks (Eric Christian Olsen) is taken into custody after "new information comes to light" about his Internal Affairs case, which had previously gone cold; Sam (LL Cool J) is arrested upon arriving at a crime scene with -- surprise! -- a dead body and cocaine in the trunk of his car; and Callen (Chris O'Donnell) suffers a similar fate when ATF agents discovered 500 lbs of explosives along with a dead body on his property.

And kicking everything off is poor Granger (Miguel Ferrer). Remember Heather, the woman he met at a bar in an attempt to track down the mole a few weeks ago? Well, he wakes up in her apartment after apparently being drugged, and finds her unconscious and badly beaten. Unfortunately, police bust down the door at the precise moment he's kneeling over her limp body, so he's arrested for that -- and then later stabbed in jail as he's being transferred.

NCIS: LA Mega Buzz: Is someone leaving?

Also, as Kensi's (Daniela Ruah) interrogating Heather after springing her from the hospital, Heather tells her via Morse code that she's working for the CIA.

All this begs the question: What in the world is going on? Well, it's no coincidence that Hetty's (Linda Hunt) 90-day deadline to expose the mole just happens to be up on the very day her agents start getting cuffed, in what seems to be a coordinated attack from various agencies. So, who's pulling the strings?

Initially, all signs point to Corbin Duggan (Jackson Hurst), the slimy Under Secretary of Defense who's back this week to gleefully collect Hetty's badge. Hetty eventually realizes that Duggan exposing the mole himself would be an even bigger boon to his career than taking her down, making him Suspect No. 1 in her eyes. But that theory's blown out of the water when Duggan goes out to meet an FBI SWAT team as it descends on the NCIS office and is promptly gunned down by a sniper. Kensi and Hetty make a watery exit just as the SWAT team enters the office.

Meanwhile, amidst all the chaos, Deeks is trying to plan a (third? fourth? I've lost track at this point) proposal for Kensi, and is trying to find the perfect LA location to pop the question. So at least we've got that to look forward to when the mole investigation concludes.

So, NCIS: LA fans, what are your theories about who's behind the arrests? Share your thoughts in the comments!

NCIS: LA airs Sundays at 8/7c on CBS.

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