Rifts were opening up
inside Par Vollen. The qunari could kill the demons but not close the rifts. More were opening up, and so they had no choice but to call for the Inquisitor's help because the rifts had to be closed.
Inquisitor didn't want to go, but Bull still cares about his people. Bull refuses to let the Inquisitor go alone, though, because he was like 98% sure that they would turn on him when the rifts were closed. Qunari were absolutely pissed that Bull was coming, threatened to bar them from the city, but Inquisitor sticks to his guns. (He took Dorian too, so the three of them, Tal-Vashoth, Tevinter Mage, and Dalish mage, were all pretty much going "WELP WE FUXD.")
They land, decide it's a matter of going in, closing the rifts, and going out. Cole is their ace in a hole if something goes wrong, because no one knows that he is there. They march in, argue with the qunari, then eventually get to the rifts. They close one, and as soon as they do it, some guy bursts from the crowd, screaming tevinter as he uses some kind of artifact to open another rift, then suicide blood-magic's to summon a pride demon onto the crowd before the qunari guards can get to him.
Annnnnd everyone shits bricks because this isn't going to be a quick in and out before we get qamek'd thing, if there are venatori within Par Vollen itself.