When I turn in the quest "Diplomatic Immunity," Dephine should give me a new quest called "A Cornered Rat." So says the strategy guide, at least. The problem is that she doesn't give me the quest.

I'm told that prior involvement with the Thieves Guild quest line messes this up. So the only thing I can think of is to complete all of the Thieves Guild quests and then see if that resets Delphine. Has anyone with this bug tried this?