This is The Silver Doe from Deathly Hallows, but I felt it should be told from Snape's point of view... let me take you to the wintry Forest of Dean, when a mysterious silver doe leads Harry to the Sword of Gryffindor, and one leads Ron to Harry...
Disclaimer: I don't own any of these characters, J. K. Rowling does, and she gets all the money. I just have fun with it.