All of the stores were closing early, which suited Crookshanks just fine. He knew tonight would be the night of the explosions and bright lights in the air, and he was able to convince the stray cats that Arabella fed behind her grocery store to help him with his hunt. It had taken some considerable effort to get Narcissa to teach him how to recognize the letters, but there was nothing there about Regulus. That's why all the cats were needed tonight.