This quest begins immediately after Storming the Walls. Now that Sigurd has finally been rescued, it’s time to speak with him at Ravensthorpe.
You’ll find Sigurd at the longhouse in Ravensthorpe. When you enter it, a cutscene will begin. You’ll find that Sigurd isn’t behaving like the man you once knew. When the cutscene is over, take some time to speak with Basim and Randvi in the longhouse. After that, speak with Sigurd in the graveyard to the west of the longhouse. A cutscene will begin, after which the quest will complete.