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Dunno if this was posted before, but if you search arhu's chambers near the cathedral and read his diary in the chest, kemm will show up with a bunch of paladins (more than 10 of them) and if you fail speech check you can choose to fight them all and get a massive amount of xp, like more than a million, arhu's quest will update with a red flag pointing to kemm's vault.
There is a very good technique for fight with Kemm. As he is most powerful of the whole group wait for him to cast phoenix dive and in next turn use on him teleport ability. I got it even with my fighter as it needs only 2 points in aero so you can get it on equipment easily. there are two spots on this map where if you teleport him he won't be able to attack until cd on phoenix dive will go off. One is behind source container although you cannot target him with ranged attack there. Another one is on the right side of the stairs, blocked with torture bed. He won't be able to move from there either and you can target him with bow (but be careful as he has deflect ability from his shield all the time so the damage will hit also your archer). Once you deal with the rest of the group you can finish Kemm easily.