I decieded to be very subtle. When I picked Joanne up from her library job that evening, I suggested we grab some dinner at a nice little restuarant we liked. It wasn't easy to covince her that she could get away with not heading straight home and studying, but I managed it.
Near the end of the meal, Joanne went to the bathroom and I seized the opportunity. I pulled the little bottle out and wondered how much to add. I decieded to play it safe and add just a little. I was tempted to pour it all in, but that might cause quite a scene. And besides, if a little worked, that meant I'd have plenty for the next couple times.
Joanne returned a few minutes later and suspected nothing. The liquid was clear and presumably tasteless. We finished our drinks and left. As we got back into my car, Joanne was already acting much less serious (she'd talked mostly over dinner about upcoming tests and class assignments).
She let her hair down and snuggled against me as I drove, nibbling on my ear and kissing my neck. I wouldn't have minded more, but that would've made driving less than easy. I guess I'd used the right amount of aphrodesiac.
"Lets go for a walk on the beach" she quietly suggested, her voice hinting at more than just a walk. I headed for the nearest deserted beach I knew of.
She was out of the car before me, playfully pulling me toward over the dunes and out onto the beach. I glanced around, but saw nobody. In fact, the only light came from the full moon.
We quickly ended up on the sand, tongues dancing and clothing slowly working its way free. We rolled over and into the incoming tide. Our shoes were off, as was my shirt and belt. Her blouse was unbuttoned and almost off when a small wave knocked me of of Joanne. As we lay side by side on the wet sand, she closed her eyes and moaned slightly. "My legs..."
I looked down at her legs, which had started to turn black, almost the same color as her hair. I touched one and she moaned softly again. Her leg felt strange, no longer like a person but more like a...a...dolphin? I looked back at her face and her eyes were closed and she was smiling. I noticed her bra snap, her perky breasts increasing at least a cup size.
"Release the animal within me" she said forcefully. I quickly removed my pants and underwear. I ripped her skirt off. The blackness went up to her waist but no further. Her legs seemed to be merging together and had shredded her panties. Her slit was stil there. I entered her and she moaned. We rode the mounting waves of pleasure to a height I never though possible. I could feel her legs drawing togethering between mine. I felt something gently brush my feet then heard a slapping in rhythym with my thrusting.
Just then, we both orgasmed terrificly and I collapsed, exhausted. We stared at each other in blissful silence, having just completedly unquestionably the best sex of our lives. "All will be as you desire" the old man had said, and it was. I had wanted more sex with Joanne, but I secretly dreamed of sex with a mermaid as well, one with Joanne's looks. "This will bring out the animal in your woman" indeed!
And I still had most of the bottle left!