Find Rejiek's ally

Find Rejiek's Ally is one of two unmarked quests that are unlocked by completing the quest Solve the "skinner" murders in the Bridge District, with its existence being revealed by reading the Tanner's Letter.

Resolution
Go to Imnesvale in the Umar Hills and speak to Fael, who can be found outside of the Umar Inn during the day. Purchase a copy of History of the Zhentarim from him, and then pick the answer "Darcin Cole". He will reveal himself as Rejiek's contact, presuming you to be his ally Rejiek. If you play along, he will inform you that he requires blood from a Silver Dragon to complete the incomplete Human Flesh armor. This enters the marked quest Finish the Leather Armor begun by Rejiek Hidesman into your quests list.

If you give him the wrong list, or otherwise reveal that you are not his message contact, he runs away and you acquire nothing.