I think I love you! Seriously, this story is awesome. I loved how you so seamlessly wove the Harry Potter and Sherlock Holmes universes together. I was so happy when I saw it was Sherlock Holmes crossover as I loved the books.
I like the parallels between Holmes and Snape as well as the parallels between the bad guys in the past and the bad guys in the future. Mortdelavie = Moriarty was very clever. Agrippina made a convincing past version of Bellatrix, and though it took me a minute, I remembered that Prewett was Molly's maiden name (and Mrs. Prewett's son worked for the Ministry as well), so it was nice having her ancestor in the story as well.
The relationship between Harry and Severus was well-written and slowly developed with many bumps along the way - just the way I like it. I also like how they concealed Holmes and Watson from the Wizarding world.
There's so much I liked about this story, and I'm sure there are things that I missed. I've marked this one as a favorite so I can go back and re-read it. Excellent work!