The day passed uneventually, as the two of you relaxed at the cabin and enjoyed the good weather and not having to study or attend classes.
But toward the end of the day you began to feel oddly anxious and you weren't sure why. You decieded to go onto the cabin's back porch to watch the sunset. It was a beautiful sunset but it only seemed to increase your anxiety. As the last of the sun slipped below the horizon, you went back inside just in time for Lisa to walk out of the bedroom wearing a pink bathrobe. The color reminded you of her mermaid tail from last night. This mental connection caused a flickering of realization about your anxiety.
Smiling, Lisa walked up to you, wrapped her arms around you, and kissed you deeply and pressing her body tightly against yours. When your lips finally parted, you were completely erect. You pulled off your shirt while Lisa pulled down your pants to your ankles. She took a step back to give you a good view as she slowly pulled the tie-string free from her robe and seductively let the robe slowly slide from her shoulders to the floor.
Lisa glently pushed you back against the wall then slid herself onto you. The lovemaking against the wall picked up though something felt...off.
Lisa put her lips by your ear and whispered "I know it's calling to you because it's calling me too. It's the pond. I don't know how I know, I just do."
"Then let's go and see what happens."
You scooped up Lisa and carried her down to the pond. You waded straight in. After the first few steps, your anxiety cleared and you knew without a doubt Lisa was right. Whatever it was about the pond from the night before that had changed the two of you, it was drawing you back into the water.
You waded deeper into the pond, until Lisa was mostly underwater as well. But neither of you yet transformed.
Then a sliver of light appeared on the water's surface and you turned to see the moon begin to creep above the horizon.
"It's not just the pond, it's the full moon as well" you realize aloud.
"Yes and I can feel the changes starting. It's going to be another long night" she said with a smile.