I Can and I Will Revamped (смешанная)

This was started by a friend long ago when theories about Snape being a vampire were still rampant. Years later after college she found it, nearly threw up at the writing, and set to fixing it. Eventually it was handed over to me. I have edited and rewritten as best I could.
A potions prank is the catalyst for an unwanted change. In the mind of a man whose entire life is discipline, what happens when that iron will is tested by hunger he had staved off for so long? What steps does he take through that red mist of need and addiction to protect himself, his career, and those he has, just slightly, grown to care for?
This story starts just before Harry has come to school. It may continue into it if people like the story. Tags etc will update with story.