Disclaimer: same as the ones in the countless other HP fics. I do not own, and Harry Potter belongs to J.K Rowling.

No, not again! Minerva thought, surveying the class and the children within again and again just to make sure she didn't see wrong. Sadly, it didn't change the fact that Tonks wasn't present in today's class. The only difference from the day before yesterday was that now both she and her friend were absent.

Minerva wasn't surprised, just resigned and irritated.

She cursed in Scottish in her thoughts, but nevertheless began that day's Hufflepuff and Ravenclaw sixth year lesson, already dreading what Tonks will whip up this time.

The last time had been bad enough.

There was a knock on the door ten minutes into her lecture on how to use non-verbal casting in transfiguration. She slowly turned to face the door. Taking a bracing breath, Minerva walked briskly to the door, and opened it after a moment of barely noticeable hesitation.

It was Tonks, pink hair and all. To Minerva's relief, she looked completely normal.

"I'm sorry for being late, professor McGonagall'', she said politely. "Peeves tried to pull a prank on me on the way to class." Tonks even looked apologising. If this was another prank (which Minerva was strongly suspecting now), she was doing a bad job of trying to seem like there wasn't any prank at all.

"Go to your seat, Miss Tonks, and five points from Hufflepuff for your tardiness", Minerva said a bit snappily. She wasn't in a very good mood. Relief had all but turned into annoyance.

Tonks must have noticed that fact too, because she scuttled hurriedly to her se– no, to her friend's seat. And she didn't stumble once on the way. Minerva gave Tonks a narrow-eyed look, having been the subject of too many pranks in her time as a teacher.

And speaking about Tonks' friend, "Miss Tonks, where is Miss Williams?"

Tonks started a little. It took her a split second too much to give an answer to not look a bit fishy. "She– Ella, she had to go to the Hospital wing. Stomach ache", she told Minerva quickly.

Minerva hummed, making her student fidget . She would keep an eye on Tonks, or the Tonks-lookalike, as she suspected. The easiest way to tell if she was the real Tonks was to look for sudden changes in appearance. And that was exactly what she was going to do.

She tasked the students with practising non-verbal casting. They were supposed to try to transfigure a hedgehog to a pincushion, without a word. While they did that and hopefully didn't set anything on fire, Minerva could keep an eye on Tonks.

And that was exactly what she did.

And absolutely nothing happened.

The halfway mark of the class came and went without any fires or explosions or rocks or even a hint of feathers. It was a calm lesson this time and Minerva's shoulders were starting to relax a bit. Maybe catastrophes like the previous sixth years' class would only happen once a month.

Bang!

The door crashed in.

A Ravenclaw boy let out a scream of pure startlement, and immediately afterwards clapped a hand over his mouth, embarrassed. Every last student turned on their seats to look at the doorway.

On the fallen door was standing the Headmaster in all his blinding glory, wand in hand.

Honestly, was Minerva's incensed thoight. How was anyone supposed to be able to look at him for long periods eithout going blind? Neon pink robes with little shining green dots like small stars? Horrible.

And why on Merlin's beard couldn't he just open the door like a normal person?

"Minerva!" Albus exclaimed, out of breath. "Someone set loose a large herd of transfigured Acromantula on the third floor! We need help from all the teachers to catch them all before someone gets injured!"

Minerva spent a splitsecond standing frozen and staring at Albus wide eyed. She wouldn't, would she? was the thought circulating around her brain. But she was right there… Wasn't she?

"Minerva?"

Had she blinked at that short moment, she might have missed the momentary change of colour of in one of the many little strands of hair in Albus' beard. But as she didn't blink but instead stood like a statue, she saw it. The Headmaster, Minerva was absolutely sure, although had a lot of amazing abilities in his hands, didn't possess the ability to change his beard's colour to blue.

So it was an imposter.

"Nymphadora Tonks!" she almost shouted, though inside she wasn't as angry as she let on. She was far more relieved that no first years were going to get eaten by transfigured spiders. This was just another tasteless prank, no danger whatsoever.

"Detention for a month for impersonating the Headmaster, Miss Tonks! And thirty points from Hufflepuff!"

Tonks pouted. With Albus' face it looked peculiar, even though it wasn't far from some of the looks Minerva had seen on his face.

"I told you she would notice something was different", the Tonks-look-alike said from her seat. Minerva came to the conclusion that she was in fact Williams, Tonks' friend. She was probably under some charm. Minerva would have to give her detention too.

"You should listen to your friend for once before setting up another prank, Miss Tonks", she said, glaring in her icy way.

Internally, she could admit that it was somewhat humorous to watch someone who looked so alike the Headmaster look so obviously nervous by her stare. Gods knew that that didn't happen often with the real headmaster.

"Uh, I'm sorry, professor", Tonks said, while morphing back to her normal form at the same time. Unfortunately for Minerva's eyes, the horrendous robes stayed on her. "Won't do it again."

"I'm sure you won't", Minerva said under her breath to herself, too quiet for the children to catch. She spun around and walked back to the front of her classroom, settling herself behind her desk.

"Take your books, parchment and quill out, Miss Tonks, and write down everything on the blackboard." She paused, and then added: "Your first detention will start here after dinner. Do not be late."

Tonks walked slowly to her seat, still wearing the twinkling pink robes with little green dots on them. She didn't look like she was planning to get rid of the clothes. Where she had even gotten them, Minerva had no idea, and honestly, she didn't want to know.

On the way to her seat, she only tripped twice.

"Er… Professor?" Tonks asked carefully, but in her voice was a note of urgency. She was probably aware that Minerva wasn't in the best of moods to approach, but that urgencency in Tonks' voice was what got Minerva to pay attention to what she had to say.

"What, Miss Tonks?" she asked, voice tight.

"Uh, just that… Er, I wasn't exactly lying about the transfigured Acromantula…"

Minerva turned her to look at her so fast she almost got a whiplash. "What?" she burst out, horrified.

"Yeah…" Tonks rubbed the back of her neck. "I guess someone thought it would be a cool idea. It wasn't me!" she hurried to add at.

Minerva was already hurrying towards the doorway. She snapped out a hasty, "Class dismissed!" on her way out.

Behind her, Tonks' hair turned blue.

A.N.: Might be a multi-chapter fic

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