From The Grey House:
Charlie nodded gratefully and followed the young man down to the dungeon. After the young man locked him in a cell, Charlie started to think about all the ways he might have been able to save Natalia from being shot. As he thought about it, even if the thoughts were erratic and impossible, he grew angrier and angrier at himself. Within moments, hair started to sprout on his body. As soon as the transformation began, Charlie felt a pinprick on his neck. His hand went to the tranquilizer dart as he fell over. He was instantly asleep.
Once the werewolf was unconscious, the human put away the gun. He then went back upstairs to help Ben with the newest member of Vincent’s household.