Magical Mermaid Tail

She'd found it on an obscure website.  It promised to be the most magical experience.  She'd wanted to try a mermaid tail for a while but hadn't found the tail that she could feel was worth the money.  Of course, she had learned to monofin to get ready and was in pretty good shape because of it.  The package had arrived by courier, no less, three days later.  When it first came out of the box, she was a little disappointed.  In the box, the tail looked like thin, semi-transparent film rather than a tail sturdy enough to swim in.  Shaking it out, she noticed a book of instructions and a bottle of strangely bluish lotion.  Carefully, she uncapped the lotion and, as per the instructions, spread it thinly on her legs.  The filmy mermaid tail slid on with almost no resistance.  That's when her world changed.  She felt her insides twist as if someone were needing them.  She heard the cracking sound of bones in her legs accompanied by intense heat.  She fainted.

She awoke sometime later lying at the poolside.  The flimsy looking tail was gone and so were her legs.  In their place was the solidly piscine tail of a trout or some similar fish.  Tentatively, she tried to bend her knees to get into the pool and shrieked when the tail bent in a smooth curve rather than at the knees as she'd expected.  The tail ended just below her buttocks and she quickly discovered other changes.  On either side of her body, at the base of her ribs, she found a slippery patch that proved to be gill covers.  Once in the pool, though, she found herself revelling in the freedom of the water.  She was fast, far faster than she'd ever managed with the monofin.  She could jump, too!  The rest of the day was spent playing in the pool, being a real mermaid instead of a woman in a costume tail.  

It was only after the sun began to set that she realised there was a price to pay.  How would she get back into the house?  Beaching herself by the box, she discovered the book held no instructions for becoming a woman again.

Woman: Swift Creek Photos
Fish: Pikkatze