Two weeks later, I awoke to the sensation of weight on my lap. Or not exactly my lap, since I was still laying down in bed.
 
"Amelia, not this again," I mumbled without opening my eyes. I was still exhausted.
 
"'fraid you've got the wrong girl," Amy's voice whispered softly. Startled, I opened my eyes to see her face mere inches from mine, so close I could feel her breath on my face. I cautiously traced my eyes downward: her pajama shirt was hanging open, just barely concealing a tantalizing view of her breasts, the toned skin of her abdomen also visible in the faint light of early morning. She was straddling me, leaning forward towards me, too seductively.
 
"The hell are you doing?" I hissed under my breath.
 
She shifted her weight, intentionally teasing me by resting solidly on my crotch. I could faintly make out the sensation of her vulva pushing against me, parted ever so slightly, through just a few thin layers of fabric. This was so wrong. "I thought it might not be a bad thing to wake you up like this once in a while. Besides, I need to talk to you before I leave for work."
 
I struggled not to make my discomfort obvious, but it was in vain. I was already rock-solid, and my sister's weight was pressed right up against it. She smiled tauntingly. "I've got someone I want to introduce to Amelia. Do you think you could do me a favor?"
 
"Introduce... to her? You don't mean, like...?"
 
"Exactly." Amy shifted her weight yet again as if to emphasize her point.
 
"Look, she's not just something for you to play around in. She's MY girlfriend, and having you involved was already confusing enough for her. Now you want to bring a girlfriend along?"
 
Amy's expression softened a bit, becoming a bit more serious temporarily, and she pulled back a bit to give me a little breathing room, at both ends. "I know she's yours, but, you've gotta spare me a little slack here. I went through that experience once. You've done it how many times now? I mean, don't try and tell me you aren't inside her every chance you get."
 
I couldn't argue with that. "But bringing a friend, too? Why do you have to go that far?"
 
"Because if I didn't, it would be cheating. But oh god, I have to try that at least once more." She pushed all her weight against me now, hugging me so close it was as if I could feel every contour of her body. "It has to be soon, before she goes away to college. Please?"
 
Her imploring expression resonated with me, our eyes locked in an embrace of conflicting wills for a seeming eternity. It wasn't like I didn't understand her desire to begin with. Her desire blended with mine and ultimately I didn't have the heart to turn her down. Way to play on my weakness, Amy. "Alright, I'll talk to her. I think I might have just the right idea."
 
Finally, the pressure on my body was relieved, as Amy claimed my reluctant acceptance and stood up. "Thanks! OK, I've got to get ready for work."
 
I rubbed my forehead. "You're welcome..."
 
* * *
 
That evening I had only a short time to visit Amelia. I was already parked outside her house waiting when her own car pulled into the driveway, home from her internship. I waved nonchalantly as I stepped out, and she gestured furiously towards the front door, emphasizing how few hours we had before she had to leave again for violin lessons. I trotted up while maintaining some facade of patience, but as soon as she was inside, Amelia slammed the door, twisted the deadbolt into place, and pushed me against the door, our lips interlocking. My hands, which instinctively reached up to push back, fastened on her breasts and began to massage them.
 
One wet kiss later, she released, hiked up her pink dress, and stripped off the plain white panties beneath it. Barely breathing out the words, "Get in," she lifted my hands from her breasts, guided me by my shoulders to a kneeling position, and pressed my face towards her waiting slit. I didn't even have a chance to tease her, "Already?" before my mouth was engulfed in moistened folds of flesh.
 
With my face inside, it was like stepping onto a moving platform; everything set in motion at once. The muscles of her pussy took hold and lifted me deeper, while her hands engaged my back towards her, and gravity tugged Amelia downwards around me, her posture shifting her center of gravity forward from her feet to mine. In one breath, she slurped down my neck, bunching up my shirt. Two breaths left her spread-kneed on the ground, exhausted, while her vagina gulped down my still-shoed feet. I toppled end over end into the familiar pink cavern of her immediate insides.
 
"That was intense," I added after I had caught my breath. "Whatever happened to keeping it scientific?"
 
"I couldn't wait. Obviously." She still sounded breathless. The space I was in lifted and sank massively in rhythm with her exhalations.
 
"You couldn't even let me strip first?" I examined my clothes: already sopping, clinging awkwardly to me, feeling entirely out of place in this realm of soft moist flesh.
 
"I admit that that may have been a mistake. It didn't feel nearly as good going in."
 
"Not to mention how I'm going to explain this condition to people when I get home."
 
"Hmmmm... actually, if I throw them in the wash now, they'll probably done in time for when I have to go. Can you get them out?"
 
"I should think you would know. Let me see what I can do." I peeled my shirt off, then stripped soggy socks from my feet and tucked them into wet shoes. Finally, I dropped my pants, and rolled everything into a wad. "Okay, here comes," I said, and did my best to reach up and stuff the clothing back through the cervix-hole through which I'd come.
 
Amelia tensed for a bit, and I struggled to avoid getting flopped back through the opening as well, then relaxed again. Distantly, I heard my clothing slop to the ground.
 
"Well, that worked out. Guess I should deal with this mess. Hold on, we're moving," she said, and gravity shifted faintly as she stood up. I too stood back up, and felt out a balance where I could walk, getting my "sea legs" as it were.
 
I struck up a conversation as I began once again towards the unexplored depths. "Is it just me, or are you getting a lot stronger about, well, sucking things in? I mean, it took a lot longer and a lot more help the first couple times. This time was just, well, violent."
 
"Sorry. Um, well, I was trying to be gentler at first, but I think you're right. After all the practice we've had, I feel a lot more confident about how the whole thing works. Probably just another kind of exercise, you know?"
 
"I suppose so. Makes me wonder how big and how fast you could go, if you really set your mind to it. I bet it would be pretty crazy."
 
There was a bit of silence. I heard the creak of a washer door shut. Finally, she answered, "Yeah, to be honest, I don't really want to know. Putting a bunch of strangers and weird stuff in there just sounds... gross. And really embarrassing."
 
"I can understand that. So hey, which way should I go? Up towards the branching tunnels? Down to the deep pools? Off that one thin side tunnel I found the other day?"
 
"Ummmm... Hm, we don't have much time, so try the side tunnel for now. Oh, but on the way, can you keep your eye out for Bottles? I lost track of him in there again somewhere."
 
"Again? Yeesh, you never give him a break."
 
I could only guess that Amelia was simply blushing.
 
I spotted Bottles and picked up the stuffed animal as I found my way to the side tunnel I'd mentioned. It was narrow enough that I couldn't reach out my hands in both directions, and curved slightly to one side so that I couldn't see far ahead. I followed it uneventfully for a while before it branched; I picked one more or less at random and continued on this way for some time. Amelia began to get impatient, apparently worried that I would discover nothing of interest before I had to be expelled again.
 
"Well, if you didn't have to kick me out for your violin lessons..." I half-joked.
 
"No. Aside from how hard it would be for me to concentrate, when would I let you out? My mom's already home when I get back from lessonssssss-- teehee, that tickles!" I had interrupted by stroking an apparently sensitive protrusion from the wall.
 
The tunnel contracted around me, rubbing me all sides, and this time it was my turn to giggle. "Hey, that tickles, too!"
 
"Serves you right," she said after her body relaxed. "Anyway, it's too dangerous to let you sleep in there, like before, so you have to get out soon."
 
"Actually, about that," I started as I resumed progress through the tunnel. "I had an idea, although I have to give Amy credit for part of it."
 
"Your sister?"
 
"Yeah. It turns out she REALLY wants to do you again, but she feels bad about leaving her girlfriend out, so she wants me to bring both of them along sometime. I know that having a stranger inside of you is kind of unsavory, but I trust Amy and it's not like there aren't advantages. With three of us, it'd be a lot safer to stay in here longer. We could take turns playing lookout, and wake the others up if your body started doing anything funny."
 
"Hmm..."
 
"In fact, I came up with the perfect excuse. A weekend-long expedition through your inner world. I'd play it off like a camping trip, but we wouldn't need to tell anyone that we were actually camping out in here. Just you, me, Amy, and her mystery girlfriend. How's it sound?"
 
There was a pause as Amelia continued thinking. I decided to play my trump card. "With your internship lately, there's so little time; this could be our only chance to spend a weekend together before you go off to college."
 
"Fine, you got me. Expedition Amelia approved. You better know what you're doing here."
 
"Oh my God," I said.
 
"What? Was it that surprising?"
 
"No, it's something completely different. You're not gonna believe what I found in here."