Johnny had just opened her mouth to try and explain who she was when Ryan shushed her. "What is that?" he asked. "Who's talking?
"No!" Johnny warned. "Don't listen! It's a trap!" But Ryan was slowly stepping toward the pool, his gaze fixed on the gently rippling waters. Worse yet, Johnny could feel the pool's pull on her getting stronger as he approached it. "Stop it!" she protested, taking a tentative step towards the pool. "It's pulling me too!" But Ryan kept walking.
"Oh God, it's getting me!" Johnny shrieked. "Oh God, stop it, oh God oh..." Her voice trailed off as she walked towards the pool, staring at its inviting waves, as Ryan approached the edge. Silently, unable to tear her gaze away from the water, she continued walking as Ryan sat down and dipped a foot in. It was gradually transformed into a translucent green fin as it entered the water, the sock around it simply vanishing as they touched the surface. Ryan suddenly got a shocked expression on his face, but continued to lower himself into the pool.
Johnny knew what was going to happen, but she couldn't stop herself. There was something else moving her, and she sat down at the edge and lowered her feet into the pool, watching as they joined into a silver-blue tailfin, the clothes she'd put on only minutes before melting into nothing at the water's caress. Ryan already had his legs in up to the knee, and they had become the lower part of a scaly, emerald-green tail. He was clearly nervous now, but continued to lower himself in, as did Johnny. She didn't want to do this, but there was a powerful need in her mind that made her continue anyway.
Ryan was now in up to his waist, visibly panicking, and his lower half was completely tail now. His hips remained, giving a somewhat more human shape to his new appendage as well as providing an anchor point for its muscles, but they seemed somewhat broader than they had been. Johnny had her suspicions about what was under the slit in the front of Ryan's tail, but was too focused on getting into the pool to find out. Her legs were now changed up to the knee, and the voices of the pool had gone from soft suggestions in her mind to audible whispers - or was it just the splashing and burbling of the water? She couldn't tell.
Ryan finally shoved off the edge of the pool to drop completely underwater. Johnny somehow knew what was going to happen, and sure enough, a moment later Ryan was a confused and terrified mermaid floating a few feet below the surface. Her face was more feminine now, and framed by long golden-blonde hair which hung in the water around her head like a crazed spiderweb halo. Her clothes having been unmade by the water, Johnny could easily tell that she was fairly well-endowed, and the human part of her figure was quite slender and curvy. The only other visible changes were thin webs of skin between her fingers and gills on the sides of her neck, just below where it joined her head. Johnny was nearly as terrified as Ryan, but the overpowering drive to finish what had been started was far too strong. She was now in up to her waist and the babbling of the voices grew louder every second she delayed, until finally, unable to hold back any longer, she launched herself into the water, her own clothes disappearing, her gills and webs forming just as Ryan let out a high-pitched, bubbly scream.
As soon as Johnny was underwater, the voices ceased and she was back in control of herself. She too screamed, but more from frustration than from terror; she had managed to avoid the pool until her stupid broth-er, sister came along. She tried to scold Ryan, but the air bubbles that her lungs produced completely obscured her speech. It took her a minute to figure out that there was another sound generator in the back of her throat, but once she discovered it, she was able to produce intelligible, bubble-free underwater speech.
"Well, I hope you're happy, Ryan!" she snapped, putting her hands on her not-quite-vestigial hips. Her underwater voice was thin and even higher-pitched than her female voice, almost like a dolphin's squeal, but not as high.
Ryan stared at her, a look of stunned comprehension slowly coming across her face. "Johnny?" she gasped, managing to mimic Johnny's use of her throat-diaphragm. "Is that you?"
Johnny nodded, visibly angry. "I told you not to do that!" she said. "We might've gotten out of this place if you'd just listened!"
Ryan hung her head, her naked breasts gently bobbing with the motion. "I'm sorry," she said. "I just...I head the voices, and when I went to find them, I suddenly couldn't stop myself."
Johnny sighed, exasperated. "That's what I was trying to warn you about," she groaned. "But I guess there's no point in getting hung up about it now. The question is, where do we go from here?"
The new mermaid sisters made a survey of the pool, figuring out how to move with their tails in the process. The pool, as it turned out, was much deeper than it had seemed at first, nearly twenty feet at its deepest. At the bottom, where the drain would normally have been, was a small, dark tunnel, just wide enough for one person. The two mermaids floated above the entrance, wondering whether to risk exploring the tunnel or search for another way out.