Gah! I feel like I should know what was on the scroll, but I can't think of it!
This was a fascinating story. First off, your scene-setting in the beginning was so laden with potent imagery. I could genuinely see where Minerva was in my head, and though it may have become a bit too descriptive after a while, it was very well done indeed.
I never thought -- not once -- about Minerva being former classmates (if not quite friends) with known Death Eaters, but she would have known at least a few of them.
I thought your portrayals of both Minerva and Avery were very well done. I felt that Minerva was a young woman who was confident in her abilities but still not entirely sure of herself yet, and Avery was an impressionable young man raised to believe in pure-blood ideals and just drank the Voldemort kool-aid. There was no inherent enmity between them yet, and I liked that you made a note of that. It fit well in the timeline of Minerva's life, as well as when Voldemort was coming to power and when Grindelwald's time was nearly up.
I can't tell you how much I would love to know what happens next. I see Vorona has already entreated you in this regard, but I suppose I shall have to speculate instead.
This piece was interesting and inspired. I enjoyed it, and if a second half of it were to come out, I would definitely not be averse to reading it. :D
What? It ends there? I know this was for the Gauntlet, and submitted in 2008, so I don't suppose there's any hope of you continuing it. However, I really enjoyed it. At first, I was surprised that McGonagall didn't transform, but you made it clear why she hadn't tried that right away.
The only thing I'd look at is that in a few places you use the same words right away: for example "she flicked open the brass clasp and opened it" and "She made her way over to it, picking her way". I also didn't understand the part where she reads the letter. Did Dumbledore's name suddenly remind her what she was doing (she didn't seem to know before), or was the letter an actual explanation? I would have liked that to be clearer. Also, I didn't know that use of the Time-Turner caused momentary amnesia, so you might want to explain that.
Overall, though, the biggest problem I had was that it didn't end! I definitely got caught up in the story. You had a lot of good escalating conflict, and the characters were all in character. I particularly liked the weird relationship between Avery and McGonagall, and her response to his Fiendfyre. Very well done!