I assume you are well acclimated to the Plaguelands given the impressive taint present on your specimens. It only stands to reason that you understand how inconvenient it is for any lone member of the Royal Apothecary Society to cross the Bulwark for supplies. Renferrel claims to have an interest in bleeding hearts, the flower, in addition to once-beating hearts. I am unsure whether it is for alchemical research or their visual appeal, but I know he would appreciate a delivery of various hearts.
You receive