Like I said in a previous post, i managed to complete both quests linked to frederick (i.e. : neither of them remained active):


* i didn't give the blood stone to Frederick, so he just stand up and left.
* the imp was in Maradino's lair and i told him to stay hidden, then i gave him the potion of bravery. He left to the place where Frederick was. And when he saw the blood, he thought that his former master was dead, so he just left free.