Call Me Imshael

Ser Michel spoke of a demon named Imshael that has taken up residence in Suledin Keep. Michel has made it his mission to track down and kill this demon.

Acquisition
You need to speak with Michel de Chevin outside Sahrnia before you go to Suledin Keep. If you kill Imshael without speaking to Michel you will not be able to acquire him as your agent.

Michel will appear in front of Suledin Keep fighting Red Templars there. He'll tell you that he has to return to Sahrnia, because Imshael sent Red Templars after him, and a pack of shades now descends upon Sahrnia. He has to return to the town to protect the people there and asks you to destroy Imshael in his stead.

Walkthrough
You have to go to the upper level of Suledin Keep, fighting several groups of Red Templars and Infected Giants on your way until you finally face the choice spirit Imshael. He will talk to you first and you have the option to immediately attack him or to have a choice.

During the fight Imshael will change his appearance into several demon forms. There will be some additional opponents as well.

After killing Imshael you return to Michel at Sahrnia.

Result
Michel decides to pledge his service to the Inquisition if you killed Imshael.

Note
This can be done combined with the quest Capturing Suledin Keep.