From Protector of the Grey House:
Anthony had researched Edwin’s nightly ritual of giving his people his blood. Edwin would feed humans and vampires his blood every night. With humans, it almost always seemed to negate their will power. With vampires, it depended on their age. Anthony and Joseph seemed to think it had more to do with the person drinking the blood then the blood but were still unsure how it worked. Some who drank Edwin’s blood were affected in a similar manner as Natalia. The mayor of San Francisco drank Edwin’s blood and was very much under the Captain’s control. Joseph nodded to himself. Natalia would do anything Vincent wanted because she was under his control.
“Mierka.” There was only one thing to do. Charlie was still struggling on the ground with Natalia. Vincent was straining against Joseph’s hold. Mierka had to take Vincent to bed. Mierka turned to Joseph. “Take him. There’s no reasoning with them.”