Like so many stories, this starts with a wizard - not a bad one, not a nice one. No rookie he was, yet no archmage, but trust his peers he did not.
Where should he store all his research data, where should he write the true names of demons he discovered, where could he safely store what his creative spirit had given birth to?
This wizard, let us call him Kerlon, owned a slave-girl, sweet seventeen she was, a bag of gold did she cost, it does surprise few that the wizard made her his mistress, but ...
He thought - she is always here, and no-one suspects...and the skin, oh so soft and flawless...
An idea was born - he enchanted her back, and proceeded to tattoo all of his data there. Once the available space was used up, the spell would allow him to continue , hiding the previously written pages and making them available at notice - when none of the pages were displayed, the girl's back would be adorned by a tattooed mandala.
The girl, let us call her Columbia, had one truly unique feature - when luna displayed herself in all her glory, she sprouted wings of ivory and could fly, taking on the shape of a pigeon. This she did, and escaped from the very surprised wizard, along with all his notes - his paranoid nature lead him to burn all the originals after he had transcribed them.

One of his colleagues got wind of this, and his little eyes gleaming with greed, set out to find Columbia for himself.

The adventurers have to find that very special white pigeon until the full moon ends, as then the transformation ends, and she will be an easy target for Kerlon's enemies.

A good way to gain the favor of one wizard and the enmity of others...

For spicing it up a little bit, the GM could postulate that the girl's fear is enough to fuel some of the inscribed spells, leading to interesting situations...

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