Hmm. That could work! I like it!
I was thinking it might be Uncle. Willing to do whatever was necessary, he wanted at least one of his people captured and converted so they might later retrieve them and find a way to undo or counter the process. In fact, Cassie might have been in on the plan volunteered to be captured. Uncle and Cassie would have left Toni out of it because they knew he would have tried to stop them. It would have been an incredible risk (unless Uncle had secretly pre-conditioned Cassie to return), yet would explain he authorized so many rescue attempts for a single human before giving it up as hopeless.