Disc brake problemo

So I went on a mammoth ride yesterday in pouring rain and unseasonable high-40s weather here in Vermont. My brakes were working fine all day and then today when I went to clean my bike off (using Pedro's Bio-Cleaner), my rear disc brake decided not to work. The cable from the brake lever is pulling the caliper, but it's not catching the disc. I don't know if the pad is missing or what. Any suggestions before I have the shop guys look at it? Cheers!

If you have Avid brakes there is probably a good chance you are missing a pad. It's happened to me before, though I was lucky enough to find the pad. I now carry a spare set in my backpack, just in case!