Back to back

You walk a short distance further down the concourse, but not seeing your mother, you turn around, and head back the way you came. She probably doubled back on you, you think. You peer into each storefront as you pass it, but in none of them do you see your mother.

You almost run over your sister before you see her, you are so busy searching the stores and cafes as you pass. At the last second you notice her, standing in front of you, looking at you curiously. She has been out to the car and back, and is now holding her gym bag in front of her. She looks around, curiously. "Can't find anything to do, eh?" She grins, and you know that she doesn't expect an answer to her question. "Well ... I guess I'll see you at dinner." She walks past you, and you turn to follow her with your eyes. She turns into the hallway marked to contain showers and small enclosed sleeping quarters, and out of sight.

An idea forms in your mind, though you can certainly not claim it as your own, since it is purely your mother's. You quickly shuffle after your sister, and into the hallway. There are separate shower rooms for men and women. You step a few paces into the women's showers doorway, and peer around the wall into the room. The room contains a change machine, 8 floor-to-wall fully enclosed shower stalls, and your sister. As quietly as you can, you sneak up behind your sister as she approaches a shower stall. Luckily, there are a few stalls in use, and the white noise of the water helps cover your movements. Your sister opens up a shower stall and steps inside, and you dart in directly behind her before the door can swing shut.

Before your sister can turn around to lock the door, you press your body up against her back and grab her from behind, one hand pinning her arms to her side as the other reaches behind you and locks the door. As soon as the door is locked, you clap your hand over her mouth, muffling an annoyed sounding yell. Holding her against you, you half push, half carry her forward into the shower proper, pinning her against the wall. Your sister continues trying to yell, but your hand prevents her from making too much noise. Still clamping your hand over her mouth, you lean extra hard against her, and release her arms, so that you may quickly unfasten your pants, and pull her shorts and underwear down to her thighs. With her arms free, she tries to push you off, but from her angle she can get no leverage.

Still holding your hand over her mouth, you catch hold of both her wrists with your free hand and press them into the small of her back. As you rub your cock up and down against her ass cheeks, firming it up, you lean in and half suck, half bite her ear. Your sister lets out a moan, and you can tell that there is some amount of pleasure mixed in. When your cock firms, you begin thrusting underneath her, bumping against the edge of her pussy several times before your cock finally lines up with her lips. Again sucking on her ear, you push yourself up into your sister, and note with pleasure that she is already somewhat wet, despite her predicament. You fuck her swiftly, in short clipped strokes, not giving her time to do much but whine and squirm, though the whining sounds suspiciously like a pleasured if **** coo, and the squirming seems almost more like writhing. As you cum you fuck her even harder, slamming her against the shower wall, shooting a load up inside her. Once your orgasm finishes, you let go of her wrists and wipe your cock off on her ass cheeks.

Still holding her head, you step back slowly, then quickly turn and duck out of the shower before she can turn around. She must have figured out who was in the stall with her, but suspension of disbelief is a beautiful thing. On your way out of the shower room you tuck your juice-covered, double-emptied cock back into your pants, and zip up.