Firstly, on the question of "shalt", check out Wiktionary, which is almost always your friend:
http://en.wiktionary.org/wiki/shalt
shalt
(archaic) Second-person singular simple present form of shall.
Thou shalt not kill.
There are still some issues of grammar and tense: do you have a beta to check this for you?
The very first line is confusing:
It was like a flicker of flame in the fireplace of the dark Gryffindor Tower
This seems to say that the pair appeared in the fireplace, whereas it would make sense that they appeared in the corridor outside, at the rear of the queue.
This is a most intriguing story, with little flaws like this which make it more difficult to read, which is a pity.
Author's response
I will fix it the shalt when I rewrite the chapters. Rather get the ideas out there before they fade away.
On the flicker in the fireplace thing... I probably could be clearer when I do rewrite that part.
They appeared in the Common Room just as Percy opened the door. There was a flash of light as they crossed the diamensions from the Fairway to the common room. This flash would appear like a flicker of flame in the corner of the eye if anyone was in the room but was overpowered by the torches turning on when the door opened. Yes they appeared near the towers fireplace and not in the hall. Which is why Neville gave them a hairy eyeball (I think thats what the term is) when they joined him at the back to the group
I will fix it the shalt when I rewrite the chapters. Rather get the ideas out there before they fade away.
On the flicker in the fireplace thing... I probably could be clearer when I do rewrite that part.
They appeared in the Common Room just as Percy opened the door. There was a flash of light as they crossed the diamensions from the Fairway to the common room. This flash would appear like a flicker of flame in the corner of the eye if anyone was in the room but was overpowered by the torches turning on when the door opened. Yes they appeared near the towers fireplace and not in the hall. Which is why Neville gave them a hairy eyeball (I think thats what the term is) when they joined him at the back to the group