Lovely short, atmospheric piece; quick and dirty and rough and raw. You've perfectly captured Ron, I think, at that age where he's not quite an adult yet, but certainly no longer a kid, and out to prove himself. His growing fascination for Sirius and his desire for something of his own are fantastic. I love the way it's happening so fast that Ron can't even keep up with it mentally; his racing, scattered thoughts are incredibly well done. Oh, and by the way -- hot.
It prowls the hallways, it pokes in the corners at imaginary creatures, it swears at "That no good bloody house-elf", and then it takes off for hours, as it has done every night since they crept through the cobweb layers of this house like maggots invading an empty corpse.