Sir Ryan Trawl in the High Hall of the Radiant Heart in the Temple District will ask you to investigate a group and gain their trust. You must kill their leader and his followers. The fallen paladins are under command of Anarg.
Aid the fallen paladins. Reynald will thank you will ask you to retrieve Anarg's Cup from the High Hall of the Radiant Heart in order to gain their trust.
Return to the High Hall of the Radiant Heart in the Temple District and convince Sir Ryan Trawl that you need Anarg's Cup to gain Anarg's trust. He will give you the cup reluctantly and will ask that you return it when you have dealt with the paladins.
Return to Reynold with the cup and he will summon Anarg, who already knows that you are working for the Radiant Heart:
If you have Keldorn in party, Anarg will recognize him and immediately attack with his fellows
If you accept Anarg's offer to join the fallen, the result will be the same as above
If you decline Anarg's offer, Anarg's aggressive response that follows will cause Reynold to decry the leader's actions and leave, you will have 7250 extra exp for this one less enemy to deal with
Speak with Sir Ryan Trawl in the High Hall once more to return the cup and report your success. He will give you the Gloves of Healing and 17500 XP each as a reward and +1 point of reputation.