NCIS: Los Angeles' will hope on the emotional roller coaster for season 7's "Citadel."

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Set to air as the second episode on the season, "Citadel" has Deeks (Eric Christian Olsen) fans hyped up for the debut of the detectives elusive mother. Elsewhere, however, a much darker story line will play out.

The DEA's Talia Del Campo (Mercedes Mason) will team up with the OSP once more, but her return won't be all sunshine and roses. While Talia's banter is always a crowd pleaser and her newfound friendship with Kensi (Daniela Ruah) has Deeks all sorts of flustered, Del Campo may not be in a joking mood this fall.

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"DEA agent Talia Del Campo turns to the NCIS: Los Angeles team for help after her partner is murdered," CBS teased. "Also, after Kensi grows suspicious that Deeks is hiding something, he surprises her by introducing her to his mother (Pamela Reed)."

NCIS's Los Angeles division (almost) always gets their man, so Del Campo can rest assured that her case is in good hands. Hetty's (Linda Hunt) team is also well versed in the emotional turmoil that comes from losing an agent - Kensi in particular - so hopefully Blye can lend her pal a sympathetic ear before the episode ends.

"Citadel" will air on Sept. 28. Catch NCIS: LA when the series returns to CBS on Sept. 21 at 10 p.m. ET.

Click the video below to see a preview for the season 7 premiere, "Active Measures."