In this story Harry is involved a girl from Slytherin. There are both at Hogwarts during the Christmas break. After they go to the Kitchen together to get something to eat. They go there separate ways. Harry gets 'kidnapped'. He wakes up in a room with stone walls and no windows. He gets the feeling that dementors are outside the rooms. (In reality there was just a spell that imaites them.) A snake that he finds in the room tells him that he needs to get the room next door. Using wandless magic he makes a whole in the wall. When he gets in there he is confronted by eight or nine people in blue robes and masks. (They are really the Order of Phoenix although he doesn't know it.) He turns into a panther animagus. He attacks them. (He ends up biting Mrs. Weasley) He ends up accio his wand. He conjures a room that attaches to the ceiling of the room. He climbs up it and blows a hole in the glass ceiling. He then accio all of their wands. He waits up there on the roof. There are many more mini trails. He tries to save a kids. He conjures two look-likes from a lemon drop. He gets attacked by a huge snake that is a realtive of the one that he is carrying around. He is able to summon the Godric Sword (When he gets his blood on it the name changes to Harry Potter). Then he has to pick the real Dumbledore out of 5 of them. After he learns who his captives were he is furious. He almost hits Snape with the sword. Then when he yells that he wants to go home the swords transports him to Godric's Hallow. He ends up spending the night between his parents graves.

 

Sesc won, AFAIK. I remember everything you mention being in the fic he linked.