Hey frendo! I've been desperate to reread this; I think about it so often. It's like a great tv serial :D
You create the most interesting characters and give a lot of spice to the ones we know from canon, especially the Slytherins!
I love the refresher; how you set up the circumstances quickly is impressive. And I had forgotten about Sluggy's opinion of the Horcruxes and Merlin's Invincibility Potion, and that now is another thing for Severus to solve. Ugh!

This seriously pushes a number of Severus' buttons (we all know. how many of those he has) and he is feeling stabby."

I feel you bro!