Posting this a bit early. I have finished the project and it's been uploaded, although I'm doing an additional read-through hunting lingering text glitches.
The night of the Troll, Harry had returned to his dorm to find a package on his bed, containing an invisibility cloak.
Normally he would have told Professor Snape. But he was in disgrace over the Troll fiasco, and didn't want to risk the cloak being confiscated.
Since that night, he has been exploring the castle after hours.
One night he stumbles into a room with a magic mirror. The mirror shows him with all his friends, happy, safe, and well, and Professor Quirrell being led away by the Aurors.
He decides to share his discovery. Consequently, all of the First year Hufflepuffs, as well as his Explorer Club's fellow officers, crowd into the room to see the wonderful mirror.
At first they think it must be showing them a glorious future. But then it shows Susan her murdered family. And there is no way that that vision can be true. Hermione and Draco both figure it out, and they all come to the conclusion that it was a mean trick, and that Quirrell must have done it to taunt them.
They leave, and Albus, who had been watching, disillusioned, realizes that this demonstration had not had the result he had expected.
This is another of the new illustrations with no 2011 counterpart.