I have just posted the full story from our last adventure, you can find it here Episode 5 – The Fallen Apprentice.
In addition, among the items that you were able to gather from Kalarel’s chamber before it collapsed you found a note.
Greetings Kalarel my lord.
Although you are no longer a member of our ranks, we have an offer for you that can profit us both. During your time in this region, if you should capture any humanoids, we are eager to buy them. We have duergar allies in Thunderspire in need of slave stock. If you are interested, send an envoy back to me. My messengers will show the way.
Chief Krand of the Bloodreavers
Sting recognizes the Bloodreavers as the slave-hunting marauders that captured his family many years ago.