Someone is spying on NCIS: Los Angeles' Marty Deeks.

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"Fighting Shadows" will put the LAPD detective in some hot water, and Hetty (Linda Hunt) will be hard pressed to help him out (see video below).

The pursuant has been stockpiling information regarding Deeks (Eric Christian Olsen) - stakeout photos and the works - and they are preparing to come after the liaison with everything they have. It is unknown if the mysterious troublemaker is working in some sort of official capacity, i.e. and IA investigation, but it is clear that they will become a major problem for Deeks.

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

Penned by Andrew Bartels, "Fighting Shadows" will also stir up trouble on the Densi front. Hetty will send off alarms bells for the couple when she switches up the team's partners, pairing Callen (Chris O'Donnell) with Deeks and Sam (LL Cool J) with Kensi (Daniela Ruah). Does she know about the pair's workplace romance?

It looks like "Fighting Shadows" will be filled with more than just the usual cash of secrets.

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

Tags: NCIS: LA NCIS: Los Angeles television CBS