A Potions Master and a Potter

What if on that tragic Halloween night, the famous scar had not been placed on a young boy's forehead? What if Hagrid wasn't the one who had found Harry? What if Lily had forgiven Severus? There are many could have's and should have's to this boy's tale, but none of that matters here because this is a story of a Potions Master and a Potter who's fate was changed by a single letter.