Anna has never dealt with change well. When Anna losses her Master, she panics and shifts into her cat form, hiding in her animal mind because she doesn't have to deal with grief if she's a cat. Except nobody tells the werewolf who had been tasked with taking care of her that she's not actually a cat.
It's not bad, being treated like an animal, though. He feeds her and pets her. Maybe she could just stay like this forever. Except she's human too and she has needs that has nothing to do with food and shelter. When she takes her human form, she surprises the Werewolf Alpha with her pale skin and cat ears and long, perfect tail.
He thought there was something wrong with him for being so drawn to the small kitten he has inherited from his father. When he sees her shift to her human form, he finally understands why the Wolf in him desires her so viscerally.