Ah! One of my favorite authors, you are. Well, one of everybody's favorites :D
And this is as wonderful as anything you do. The oh-so-clever Hermione, amiably slow-on-the-uptake Ron, sweet slightly clueless Harry - but getting there! I lovelovelove *his* use of Legilimency to urge Snape on! And Snape, dark and shy and snarky and vulnerable... but summarily high-handed when needed. (I think it was that word "summarily" that clinched my authorship-suspicions. Don't ask me why, and I'm not going off to do any counting-of-content, either!)
Love, simply love, the journey to the past, the castle in Eastern Europe, Dumbledore's hopeful bequest of it to Snape, just as Harry hoped young Severus would remember: bezoar and blood-replenisher!