Oh, Deeks, what are you hiding?

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The NCIS: Los Angeles detective will be under the microscope in "Fighting Shadows," so much so that the unflappable Hetty (Linda Hunt) will be concerned for his future. Even Callen (Chris O'Donnell) will get in on the action, questioning his teammate foresight in a new extended promo (see video below).

"Don't pretend like you didn't know the risks," Callen tells a distressed Deeks (Eric Christian Olsen).

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The team's head honcho will uncover the Densi secret as episode 18 begins, switching up the long-held partner structure, but it doesn't looks like the pair's unsanctioned dating will be Deeks' biggest problem. After all, it takes two to have an intraoffice romance, and Kensi (Daniela Ruah) appears to be in the clear during "Fighting Shadows."

So, what is Deeks up to, and who keeps snapping his photo? Executive John Peter Kousakis teased the mystery on Twitter.

"What has Deeks done? Even Hetty is in a quandary," Kousakis wrote. "Who is tailing Kensi? It's a Deeks mystery. Does Hetty know?"

What do you think Deeks is hiding? We want to hear your best theory, so sound off in the comments below!

Find out more when NCIS: LA airs Mondays at 10 p.m. ET on CBS.