Looking for a Slytherin Harry Potter story.

The fic I am looking for is with Harry's first year. he is sorted into Slytherin. I only remember 1 chapter. the Chapter was called I think "Troll in the Dungeons" its Halloween and Harry choose to have dinner alone in the Slytherin Common Room. he is sitting by the fire reading a book or looking at pictures of his parents. when Snape's silver doe spell comes in and tells Harry to stay in the common room. The troll starts attacking the Slytherin Common Room door, the troll breaks in and attacks Harry. Harry is able to use magic to make a shield around himself. Snape comes in and kills the troll with the other teachers. thats all I remember PLEASE HELP!!!!