Several punctuation errors mar this story. A bit of editing would have made it flow much better.
I liked the idea of a magic nullifying field. And Moldy getting his end like that was very different. I liked that.
Some of the dialogue was jumpy - it seemed to change directions without any transition. Some narration/description of what was transpiring would be better. Also there were a couple of 'out of the blue' things that didn't make sense: The food basket that Ron took from his mother ... where did that come from?
In all a good one shot. Harry's voice started to grate on me - a whiney Harry doesn't sit well if he sounds like my 2 year old - but at the end you pulled it out.