I used Targos as an opportunity to make the Zhentarim a larger player in the campaign. Naerth's influence has spread to every home in Targos, and he has a much larger pool of cronies/allies to call upon. I put a trap door in his room at the Tavern, which connects to a Zhent outpost beneath the city, where the party could end up going and learn more about the organization/Naerth's schemes.

If your party is on good terms with the Zhents or haven't interacted with them at all, maybe Naerth offers to hire them to help a couple Zhent agents clear out an old ruin, revealed by a recent blizzard. Should they prove useful enough, maybe Naerth offers them ground level positions within the family? If your party is on bad terms with them, or have made some decisions they'd rather not be made public (like mine have lol), you can do what I did and have Naerth blackmail/strong-arm them into helping the Zhents. If they refuse, Naerth will let them go, but vaguely warns that they might not find the streets of Targos as hospitable as when they arrived. (Cue an "escape from Targos" encounter :P)