Continue forward until you come upon a larger room with plague enemies. Defeat them and power through until you reach a set of double doors. Beyond this door is this quest’s boss fight, who just so happens to be Reinald. Defeat the boss and make your way back to the Deacon to finish...
Reinald wants to chat with the young deacon, whereas Geralt suggests burning him on a pyre, which forever condemns his soul. To get the best ending for this quest, retrieve the deacon and stick to the morally grey options during the conversation, as witchers should. The choices you should...