First of all, I just realised that I swapped with you for stories set in the same time period (if you pick Reason to Fight, that is), which I found amusing.
Your description of Gellert just sitting there, reading the letter and thinking, was extremely well done. Though we don't get much insight into his thoughts, your description allows us to visualise the character well, and already to give us some knowledge about his attitude and reactions.
Your take on the relationship between Dumbledore and Grindelwald is absolutely amazing: it's obvious that matters are extremely complicated between them, with the conflicting ideas and yet the deep mutual attachment and longing for one another.
both a blessing and a curse
I think this quote sums up their relationship perfectly, even though so far it's only epistolary...
What stuns me the most, with the passage in Gellert's point of view, is that there is no dialogue -- it's only character analysis, which I personally find extremely difficult to pull off. You, on the other hand, manage it brilliantly, and everything flows very smoothly and poetically, because your description, too, is lovely.
I liked the way you included a scene through Dumbledore's eyes at the end. Again, I find him very hard to write, but, again, you wrote it flawlessly. You included his optimistic character trait very well, without making him obnoxiously chirpy, which is an easy trap to fall into. I can't help but worry about the appearance of Tom Riddle in there though, and now I wonder if Grindelwald is going to be partly responsible for his transformation into Lord Voldemort.
To be entirely honest with you, this isn't quite my cup of tea, but I'm glad I got a chance to read this, as I enjoyed more than I thought I would! You've got a very beautiful writing style, and the grammar and structure of this piece were perfect, which made the reading much better.
Thanks for the swap!