What the hell is in our Chimney?

We recently finished our basement!!!! Woooo-hooooo!!!! Jason has a little tool storage room. He went in it and when he opened the door, he heard rustling...he looked around and then WHHOOSH! Something flew up and went into our chimney hole (an extra outlet we built for someday adding a fireplace in the basement)!!! We had the hole just duct taped shut, but this sucker chewed or clawed a big hole and was hiding out. YIKES!!! Jay didn't know what it was he just screamed like a girl "It's big, it's big, it's big!!!" He was the only one that saw it...and couldn't tell what it was other than it was big and flew. We didn't know what to do, I was absolutely paniced and freaked out!!! We duct taped (an entire roll) a plate over the hole and then wedged a 2 x 4 over that. We could hear this sucker clawing at the plate trying to get us. He was mad. It was soo scarry! My dad wanted to uncover the hole and hold a pillowcase over it and catch the critter. OH-NOOOO!!!! Can you picture that image...my dad carrying a pillowcase with this wild mad critter in it, through the house and letting it go out in the woods???? No way Dad!!! I felt like moving I was so freaked by the whole thing.