Bluebeard

There was only one rule: Don't open the door.

Her lord husband had been very clear: she could enter any room in the castle... except the blue door at the far end, opened only by the smallest key.

Ariane was curious, but her husband was entitled to his privacy, and there were countless other rooms to explore while her husband was away.

She set the key aside so she couldn't use it.

It was a shame that Ariane hadn't actually been able to put off inviting her family to visit until her husband returned.

Annette might be older than her by a year, but she often acted as a child much younger, and telling her something was forbidden was like waving a red flag in a bullpen. Ariane's brothers loved nothing more than causing chaos that someone else would be blamed for.

No sooner had she mentioned the key, than Annette grabbed for it, and all three took off running.

Ariane saw her husband's carriage returning, and went to meet it.

Conomor dismounted, and Ariane fell to her knees. "Forgive me, I tried to stop them from opening the blue door..."

He raised her to her feet. "You did not witness what lies beyond?"

She shook her head. He smiled. "Then my surprise is preseverved, though for breaking my rule, their lives will not be."

Ariane smiled. It was not kind. "I had hoped that you would say so."

Magic rippled, and screams echoed from where her siblings had opened the blue door. On a light breeze, Ariane smelled the scent of blood and death. She inhaled slowly, relishing the taste.

The full moon was rising, and Conomor's mane of hair thickened. "A wedding feast, for my new bride..."

Ariane smiled with teeth as sharp as fangs. "An excellent beginning."

Story count: exactly 300 words.

One of the most likely historical sources for the legend of Bluebeard was the Breton King Conomor the Accursed, locally 'known' to be a werewolf, and the husband of Saint Tryphine.

That got me thinking about alternate reasons for the murdered wives, and a story where the nameless wife wasn't a passive victim, and this microfiction was born.