While you were fighting the Guardsmen of the Inquisition, the spy noticed something important. Talk to him to know what it is.
After all, he managed to spot the mastermind behind the Inquisition invasion. Eliminating this menace would ruin all the plans the Inquisition has. So this becomes your new task.
Now you should walk back down the hill where the Spy is camped and run west until you reach a lake. Head south and then west along the lake’s edge until you find Inquisitor Ortlewyn standing on the bank.
The Inquisitor was spotted - he is hiding in the shadow of the trees near the lake.
You should talk to him. Maybe he would tell you something about the Inquisition plans... most probably not, but it won't hurt to try.
As expected, he mumbled some nonscence and tried to kill you. That was very stupid of him. What a mastermind could make such a mistake? But anyway, he's dead now. So you can inform the Lumen Priests of the Noriath Temple, who were opposing the Inquisition, that the threat has been eliminated.
To get to the Temple you should head east back to the road, and then follow it all the way north until you reach the gate.
Lumen Priest Benewion, who was mentioned by the spy, can be found a bit east of the Temple itself, next to the priests' house.
Of course he would be glad to hear that nothing threatens him and his fellow priests anymore.
Benewion was happy to hear the news and rewarded you for your help. Your crusade against the Inquisition in Noriath's Corner is over now.