"All turn to page thirteen of the textbook," Professor Snape said in his usual drawl.

Anna leafed through the pages of her book until she reached page twelve, then cautiously turned the final page, reluctant to have to do so at all. It was a bad omen - she was sure of it, something would happen today.

She scanned over the recipe, and went with the rest of the class to collect the appropriate ingredients and utensils from the cupboard. All seemed to be going smoothly enough, until she reached the part about fairy wings.

Exactly 13 fairy wings.

She pursed her lips with irritation. What could one more do? Carefully she counted out the transparent little flakes and dropped them into the potion. As she reached the thirteenth she hesitated, then pinching two at once with her silver tweezers, she dropped them both in and watched them sink.

As they touched the bottom of the cauldron the potion immediately turned an opaque mucky grey and soon billows of ashy green smoke began to roll off the top. She coughed as it caught in her throat, then jumped as Snape spoke directly behind her,

"Ruined, Miss Judaius. You will receive no mark for this assignment, and a week's worth of detentions. Perhaps that will teach you not to intentionally sabotage your own work." He cast a cleansing charm over her shoulder, effectively vanishing the mess from her cauldron, before striding away... no doubt to jump upon other unsuspecting students in their moments of mishap, she thought.

She hated Snape. He was her head of house, but he didn't seem to spare her any favouritism as he did for many of the other Slytherin students. Potions was even her best subject, and none of her fellow classmates could outdo her when it came to brewing a wicked love potion, or potent dose of Veritaserum. So what if she messed up the occasional recipe, it was stupid to add thirteen of something anyway – potions like that could never lead to anything good.

She slumped dejectedly on her stool and waited for the bell to ring. Just before it did, Professor Snape was at her elbow again.

"You will serve your detentions at precisely 1 o'clock beginning tomorrow. Tardiness will not be tolerated." She caught his meaning, but still said hopefully,

"In the morning?"

"In the afternoon," he said witheringly. She shot a poisonous glare at his back as he walked away. How had he known anyway? Grabbing her stuff she marched out of the classroom, already plotting ways that she might avoid being there at 13:00 hours, lest more misfortune befall her as a result.

The following afternoon Anna stood outside Professor Snape's door fidgeting uncomfortably from one foot to the other, and casting the occasional tempus charm to check the time. The magical clock showed 12:47. She had deliberately turned up early, but upon arrival had found the usually unlocked classroom door sealed shut. With time to reflect, she mentally kicked herself for not coming up with something more creative. She was stupid to think that Snape would be so easy to outwit.

Inside Severus patiently watched the minutes tick by. Of course he knew Anna Judaius was waiting outside. He'd noticed her triskaidekaphobia some weeks before and had been waiting for an opportunity to try and rid her of it once and for all.

In truth, she was perhaps the most exceptional student he had ever had the displeasure of teaching throughout all his years as the Potions Professor in Hogwarts. She had a natural affinity for brewing which he could only compare to his own when he had been her age. She was accurate and precise, she followed the recipes to a tee, she had no difficulty understanding the different ways to mix and stir, and she never asked for him to clarify the origin of a particular root or leaf but recognised it herself almost instinctually it seemed.

At first, her occasional slip-ups and clumsy mistakes had made him reconsider whether she was indeed as promising as he'd initially thought, but after careful examination he had detected the problem. With stony resolve, he'd decided that he would be damned if he'd let anything as ridiculous as superstition ruin the chances of one of his house - especially one like this.

The minute hand on the magical clock that floated before him finally ticked around to 1 o'clock, and so with a flick of his wand he brushed it from the air and unlocked the door. As it swung inwards though, he found that all it revealed was a now empty hall way.

So this wasn't going to be as easy as he'd hoped, but his will was strong. He would cure her of her silliness, and one day she would appreciate why. After all, every good potions master had to brew at least one batch of Baneberry, and she wouldn't be doing that with fourteen moonseeds.

Written for: the 'NEW Triwizard Tournament' Competition. Prompt: triskaidekaphobia.

Disclaimer: I do not own Harry Potter.

CC cover image (entitled 'Potions Classroom') courtesy of Rob Young on Flickr.

A/N: This is about an OC, because I couldn't imagine which of the existing characters would be afraid of the number 13. Hope she turned out ok :) Let me know what you think! GG x