Vertigo

The door opens and the woman walks in. She stands above the debilitated Caroline, and smacks her tongue with disappointment.

"You only had to do what I said, Caroline. You only had to obey. Eve's in no danger, I'm monitoring her vitals. I'm not in the habit of shattering my beautiful new toys."

She kneels down, and Caroline feels a syringe poking her thigh. "Please... I'm sorry..."

"It's too late for that. You disobeyed me Caroline, and, as it was with Lot, the punishment will fall on the one you hold dearest."

--

Caroline awakens on her side of the wall, with the woman standing next to her. She tries to speak, but can't. She's been gagged. Her position's different too; she's been tied down on her hands and knees, laying on her stomach on top of the heavily modified chair. Back arched, ass up. Familiar.

"Good morning! Sleep well? You've been out all night." The woman pushes a straw to her mouth again. Tastes sweet. "I'm sorry to say, but since you can't seem to follow simple instructions, we're going to have to start all over again today. You know how it goes by now; your first task will be to orgasm while watching Eve, so let's see how she's doing, yes?"

The woman once more walks over to the control panel, and with the flip of a switch lets light shine through the mirror-wall. Eve's in a new position as well, still on her back but with her legs in stirrups. Two thick rubber shafts are filling up both her holes, and some sort of tube is hugging her clit tightly, but everything's still, unmoving. Then, for just a moment, the pistons and the tube vibrate in unison and they are powerful. The vibrations spread through her thighs and up her belly, ripples clearly visible in her skin. Then they shut off, and Eve yanks in frustration at her bonds.

"While you slept, mommy, I've been keeping her on edge. All night. It doesn't take more than a few seconds for the machine to push her to the brink of orgasm now. Oh, how delicious she looks, don't you agree?"

The woman walks behind Caroline, and runs a fingertip between her cheeks. "Don't worry, I will let her come. She'll come as soon as you do, mommy. So you're going to have to help me out, yes? No fighting it today." The tip teases her sphincter, and Caroline yelps through her gag when the tight little entrance yields under pressure, allowing a well lubed finger to slip inside her ass.

"Now let's see how long it takes to work my hand inside this hole."

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Special thanks to @CalebZhass for their feedback and help on this story!