Speak with Jace Darkweaver and then use your Spectral Sight ability to scan the cave for hidden demons.
Jace Darkweaver swears that for a split second he sensed a demonic presence up and behind us. He took some of our forces up to the cave just to the southeast to investigate. They found nothing in the cave, but he is certain that something is amiss. Would you lend him your guidance, and more importantly, your spectral sight?