Well, Astrid believes that the jester Cicero is plotting against the Sanctuary, so we will have to go hide in the Night Mother’s coffin to try and eavesdrop on the conversation.
Getting to the room is a matter of following the objective arrow, but it isn’t hard. The room will be empty when you arrive, so go in and open the coffin of the Night Mother and step towards it. The rest will take care of itself. Cicero will come in and start talking, so just stay put and listen. Before long, the Night Mother will be talking with YOU and as luck would have it Cicero will open the coffin and discover you!
Go through the dialog options here with Cicero and Astrid (you only have limited dialog options anyway). In the end this news of you being the next Listener (which has Cicero delighted) is a bit too much for Astrid to handle, so in order to give herself time to think she wants you to go talk to Nazir to accept some new contracts.
Go talk to Nazir and accept the quests " Contract: Kill Lurbuk " (an orcish bard) and " Contract: Kill Hern " (A Vampire who’s usually with his lady vampire). After accepting those two quests, you will have completed " Whispers in the Dark ".