She looks like a young girl

At first you think it's a young girl until you see the rack she's got. The woman can't be more than five feet tall and barely a hundred pounds, but she's got tits that should tip her over. You never slow in your plundering of Kelly's cunt, but you watch the onlooker. She has a hand in her shirt and one in her skirt as she fondles herself, quivering. As you gaze at her, her body shakes and wiggles as she comes silently.

Being watched turns you on even more than you already are, and you groan as you pump Kelly full of your hot cream. She grabs your head and kisses you as you both come. You double the rate that you thrust into her. Kelly's cunt squeezes you one last time, and you both collapse in a sweaty pile.

When you recover enough to look up, the voyeur is gone.

"What's the matter? Did you see something?" Kelly asks.

"I thought I did, but it was nothing. You were great, Kelly. Stop by in the basement, if you're back in the building again." You get your clothes on as she does as well. You kiss her before you leave. She picks up a paint roller as you head out the door.

When you get out into the hall, there's no one out there.