"Sure," I said, a little warily. I could never be quite sure what Vanessa was up to. The fact that she was waving around a mysterious vial didn't put me at ease.
"This, first," she said. She smiled and thrust the vial at my face.
"What is this?"
"Oh, you'll see. You'll like it, though. Go ahead and give it a shot."
There was never any arguing with her. Besides, she wasn't the type to put me in actual danger. I took a swig and handed the vial back.
"Feel any different?"
I shrugged. "Not really." Suddenly, though, my stomach gurgled violently. "What was that?"
"Just something to make things a little more... interesting. Oh, look. I think it's starting already." She was pointing at my feet.
I looked down, and my eyes widened. A few moments ago, I'd had on light brown oxfords, but they were suddenly shifting and changing before my eyes... into a tiny black pair of pumps. My jeans, too, looked like they were shrinking, rolling back up my legs, which I saw had become oddly hairless. "What did you do to me?"
She didn't answer, but I knew. My stomach had started contracting, which caused me to bend over double as my hips widened and my thighs and butt suddenly accumulated little fat deposits. My upper body was shrinking, though, my shoulders narrower than their previous width, all my biceps and forearm muscles disintegrating. The sleeves of my t-shirt had, like my jeans, started retracting, up my arms until I was wearing a strange sleeveless bit that was slowly tightening to my body. I could feel changes to my face as my features became softer, my nose smaller, my cheeks rounder, my skin smoother. I felt hair tickling the back of my neck and reached back to find that a short blonde bob now dangled just above my shoulders. My neck had become thinner, and I resisted the urge to speak for fear of what I would sound like.
My clothes hadn't stopped shifting. Both my jeans and shirt were changing color, to a muted lilac, and were fusing together. My jeans were above my knees, then about mid thigh, and pleats replaced denim as I realized I was now wearing a simple dress. The shape in my chest and crotch area looked all wrong... until it didn't. I felt my penis shrinking and then gasped -- it sounded more breathy than I'd intended -- as it completely disappeared. My chest, meanwhile, was swelling out, and I felt, out of nowhere, the constricting feel of a bra holding back my new breasts.
I looked up (up! I must have shrunk six inches) at Vanessa, who was smiling mysteriously. She had turned me into a girl!