The six mermaids swam together, racing currents, making out and occasionally embracing a human stereotype and playing with sea creatures, using their songs to temporarily entrance them. It was temporary, and so as long the mermaid fed the creature to make up for the non-survival based energy use, it was also harmless.
Lorelei was finishing feeding a school of sardines that had joined her in an exotic, and rather erotic, dance for her lover when she heard it. It being the song that begged all mermaids to save a sister that was trapped on land. After a number of cases where captured mermaids were forced to sing, a particularly powerful mermage implanted a number of songs into to the instinctive make up of all new mermaids, particularly those who were once human, as they were at the greatest risk of capture.
In this case, there was barely a audible precursor to the full song, a sign that the singers weren't sure about the specifics of the threat but as the six of them frantically swam towards the source, it changed to the much clearer verses of the song for "injured and trapped ashore".
There was a gasp to her right as Clarissa, the best at analysing of sounds originating from out of the water, "It's a duet! I think it is those two cuties from earlier!"
"Mina and Corey?!" Barbara puffed. She'd been showing off before the song started and hadn't got her water back before their mad dash, "Why can they Sing?"
"Has anyone here ever done a temporary change on a full moon?" There was enough of a tremble that it wasn't immediately obvious that it was the stoic Kelly that asked, "Me and Lorelei haven't, but I just realised that it might have had an effect." Before anyone could answer, they had gotten close enough that instinct had taken over. The 6 began their detection spells, each slightly different and layered over one another for maximum efficiency.
"There's one human moving away from us along the beach, a jogger, I think."
"No boats nearby."
"The storefront is waking up, but that shouldn't be a problem."
"What is a problem is the cove... The song stopping means that the singers should know we're close and aren't in immediate danger, but all we're getting is fuzz from inside the cove. It feels like two somethings with magic are straddling two humans."
"We should get in there! This is our fault!"
Lorelei agreed with every point, especially the last one. There was a niggling doubt whispered that it was a magical monster mimicking a Song, but there was no time for hesitation. "Let's go..."
The mad dash had stopped when they were looking around and now it had become a slow, near silent glide towards where the singing had come from. The sun was starting to peek over the horizon but it'd take time before it was clearly visible over the town.
"I...I'm scared Millie..." "Me too, Corey..." "It was beautiful...YOU were beautiful...b-but..." "I'm know. We'll figure this out... even if we need to say here for a year waiting on those mermaids." The tears were obvious in their words and there was a protective anger in Millie's voice.
Their wait was a bit shorter than a year, as the 6 mermaids emerged sheepishly from the water as soon as she had said it.