Onyx made sure the coast was clear, then stepped through the gates of the Institute. She went up to the door, and it opened. Isabelle Lightwood ushered her in. "About time you got here. Just in time for dinner." Isabelle said. Onyx looked at her. "Um...Who's cooking?" she asked hesitantly. "I am!" Isabelle said, pushing her in from behind. Onyx's mind whirled. "I can't, I'm meeting someone for dinner." Izzy eyed her suspiciously, and Onyx gave her innocent eyes. Izzy shook her head. Onyx realised that she was still holding the cat, and put him down. Magnus changed back, and glared at her with his cat eyes. "What, prey tell, was that for?" he asked, examining his nails in a rather prim way. She glared right back at him. "Um, maybe, for appearing randomly in front of a Mundane?" she said, raising an eyebrow.
(Have you read all of the books?)