As Mark swirled his tongue faster and I drew my other leg up and, crossing them, forced Mark's face even deeper between my legs. As I felt the orgasm getting closer, I reached down and spread myself open. I moaned loudly as I felt Mark take my clit into his mouth.

"That's it! Suck it! Suck your sister's clit, Mark! Get her off right in your face, all over that smug face of yours! Prove that tongue's good for something besides whining. Oh oh..."

I gasped as I felt the orgasm beginning to race through me. I arched my back off the desk and pulled on the belt, pinning my...