You turn to look in the same direction as Lydia and are shocked to see Monica was now naked, with a bubblegum-pink fish tail. Monica was a mermaid too - but how? She was staring daggers at the both of you.
Before either of you could really process this new development, there was excited shout followed by a splash as one of the intoxicated partygoers jumped into the deep end of the pool. He had been inside and had missed the altercation, and drunkenly thought a pool party had broken out. Soon others were jumping, sliding, or being pushed or thrown into the pool as well. Some were still in their formal wear from prom while others stripped down to their undergarments.
You were grateful for the distraction and carried Lydia out of the pool via the stairs in the shallow end.
"Where to?" you asked.
"The beach" replied Lydia.
You carried her down a short boardwalk from the house to the beach. Looking around, you found it dark and empty. You carried Lydia a few houses down, picking one with no lights on and a large boardwalk. The noise of Monica's party was still faintly audible. You carefully set Lydia on the sand. Collapsing on the sand next to her, you saw a tailfin peeking out from the bottom of her dress. You realized you didn't have long to go before you would transform as well.