Sorry for the delay, been cat searching. And stumbled onto a bigger mystery

I opened my basement door Monday night to grab the trash and suddenly saw a cat take off running down the stairs into the basement. I was fighting a bad cold, so I poked my head down there and looked around, but didn't stay long. Left the cat some food and water, and figured it would be easier to find with some help from daylight. Went downstairs yesterday during the day, and still no cat. After giving up, left more food and water. This time, the cat hasn't really eaten any of it. I went back down today, and really gave the place a good solid once over. Took Malia with me, to see if she could hunt the cat down. Still no cat, but I did find a mysterious hole in the back wall that is covered up by a piece of plywood. I pulled the plywood back a ways and saw that there were old birthday cards in there. My curiosity is killing me, but so is my cough, so I can't really do any high intensity exploring yet in the superdusty basement. But once I get all the way over this cough, I will pull back the plywood and let you know what I find there. It will be a lot like when Geraldo opened Capone's safe. In the meantime, I'm hoping that the cat somehow got back out the way he got in (through a cracked window), because I don't know what else to do. Perhaps we should form a cat-search team and meet down there after the Phils game tonight.