The Storm and what Came Before It is an Act 3 companion quest for Varric in Dragon Age II.
Acquisition
Received at the beginning of Act 3.
Walkthrough
Speak with Varric in his suite at the Hanged Man.
Varric and Anders are swapping tall tales when you arrive. Anders leaves, and you have a short chat with Varric. He talks about the power vacuum and issues in Lowtown, but there is no relationship effect.
Bugs
Even if you told Anders to leave Kirkwall during Act 2 and he is neither at his clinic nor are you able to use him in your party (which would lead to the assumption that he has not yet returned for Act 3) he may still be there talking to Varric during this quest.
Trivia
Anders will be telling Varric stories about the Blackmarsh, which was a location and main quest line in Dragon Age: Origins - Awakening (and coincidentally, where the The Warden-Commander first encounters Justice)