The prompt I'm using is to write a Dark!AU for any lightside witch. It's from assignment 14 of History of Magic, for Hogwarts School of Witchcraft & Wizardry (Challenges & Assignments).
Disclaimer: I don't own Harry Potter.
Minerva McGonagall was an intelligent woman, there was no doubt. So when she was informed of her newest partner – well, she had good reason to be hesitant.
The woman smiled brightly at her, "Why, hello, Minerva, fancy running into you here." The words were punctuated by a small laugh as she took a seat. "When he told me I would be working with another double agent, I would never have suspected you. You're an incredible actress."
"Thank you." Her tone was drenched in politeness as she analyzed the witch before her. While she may have been complementing her acting, it was nothing compared to this woman's. Dumbledore would have a field day, should she ever tell him. Perhaps she would. "As are you."
She moved over to the doorway, assuring herself that they were, indeed, alone. "Has Dumbledore put you up to this?"
"That depends," her friend's smile shifted into more of a grimace. "Has he put you up to this?"
Either answer could destroy her. The woman knew that. The question was impossible to answer correctly, not without knowing the other's answer. They were at a standstill and they would be there until one of them were willing to take the leap of faith. It wouldn't be her.
"I don't think that's any of your business. You could ask him, but then so could I."
Brown eyes examined Minerva cautiously. "Alright, it looks as though blind trust is the way we're going to be doing this. Excellent."
Her chin dipped in a curt nod. "Let's do the job, then."
"After you." The grin was back. It wasn't like her usual smiles, the ones reserved for her before. It was malicious, promising utter destruction if she slipped up one way or the other. She wondered if the woman was truly against Dumbledore now. If so, how did it even happen? Had it been a trick the whole time? It was also possible that she was doing this on Dumbledore's orders, though. Who should she tell? Dumbledore or Voldemort? Telling Dumbledore could be a one-way ticket to destruction, if she truly was on his side. Plus she had a lot of allies who would likely take her side. Telling Voldemort – he wasn't an understanding man. If she was wrong…
She looked over at her companion, seeing similar thoughts swirling in her eyes. "We're to capture the suspected member of the Order." She ignored the fact that, between the two, there really wasn't any speculation, any doubt. They both knew that the man wasn't a member, but it was a fact that both of them glossed over. "Then we're to bring him to the Dark Lord, to receive proper punishment for his transgressions."
Molly Weasley nodded. "Let's get to it, then. I believe my family would really appreciate it if I were back in time to fix dinner; the kids are about to return to school, you see."
Minerva's lips thinned. This was a complication that she really could have done without. "I see."
I just couldn't resist. My initial choice was Minerva, but then I thought it would be pretty surprising for it to be Molly, of all people. I really wanted to do both. I didn't want to go into their reasoning, so instead I made it kind of ambiguous as to which side they're on. In my mind it qualifies because they're both doing Dark things, even if they aren't explicitly a part of the Dark side specifically – and they might be. That's up to the readers to decide for themselves. I'm really not sure what genres this fits, so if you have any ideas, please tell me.
The total word count is 502. Enjoy!