From Protector of the Grey House:
Joseph let the comment pass, as there was more to puzzle out. “What about this morning Natalia? Were you tired when you woke up?”
“I suppose I was. What are you thinking?”
“I believe your will was susceptible to control due to the circumstances of this evening. You were tired after your three days as a captive. You lost blood to Wayne and then before you were completely healed, Vincent took more and most probably kept you up long after sunrise, correct?”
Natalia nodded. They had been up until past noon making love.
“Then when you woke, you had a battle of wills with Anthony. He must have been hard to control. I saw you when you entered the training room. You looked exhausted.”
She nodded again, as her hands went to her head to massage her temples.
Joseph stood and went to the bed he shared with Mierka. He sat behind Natalia to massage her shoulders, neck and temples. She sighed, and relaxed as his fingers loosened her muscles. “This is how I see the events of the evening. You were tired, your will was battered and the vampire you love, and trust fed you his blood. We have learned that a vampire’s blood can be used to control other vampires, but it seems to work better on humans. I believe that had he fed you his blood on any other night, you may not have been affected. It is also possible that he may be the only one who would be able to.”
Joseph leaned in to whisper in her ear. “You have been with him for seven years. When was the last time you denied him anything Natalia? You trust that he will keep you well and operate on the knowledge that he will not harm you unless you harm him. He is your love, Natalia. We all know this. He can control you because you allow it.”