Finals came and went. Flitwick's involved Wingardium Leviosa, McGonagall had the class turn mice into snuffboxes, and Snape had them brewing forgetfulness potions. Binns had the class answer 55 multiple choice questions about wizarding history before 600 BC, followed by 3 short answer questions, 1 document-based essay, and 1 long essay. This rather long final took four days to complete. Hagrid had conveniently made one of the questions in the written portion of his final about Cerberus, so the trio figured out how to get past him because they had studied Cerberus well, both in the "field" and in his class.
The friends decided to act that night. Harry and the group all set off from their respective common rooms and met up at the corridor where Cerberus was. The way to calm him down, according to the class and final, was to play the flute. So Harry also brought his flute with him. Harry played Concert F for a while until Cerberus eventually fell asleep.
When they opened the trapdoor, they all fell into a room full of a plant called Devil's Snare. Maud recalled this from herbology class. "I know how to counter," she said, "On the count of 3, cast Lumos." "One, two, three, LUMOS!" everyone complied, and the Devil's Snare was defeated.
Next thing they knew, they were in a room of floating keys. "Quick, find one!" cried Hermione. Enid noticed the lock on the door. "Look for an old fashioned silvery one, like the lock," she suggested. There so happened to be broomsticks in the corner, and everyone took one and flew into the air looking for the keys Enid had suggested. They eventually found the one key they were looking for, but it was a hard one to catch, as it wanted to avoid them. Ron dived, Hermione rocketed up, Harry streaked after it, and Mildred, Maud, and Enid all tried to surround it so it couldn't go anywhere. Harry would catch it in the end, and the key did indeed open the door that was at the other end of the room.
In the next room, a game of chess had to be played. Ron and Enid became knights, Harry and Mildred became bishops, and Hermione and Maud became rooks. A white pawn moved forward two squares. Ron took charge and directed the black pieces on what to do. The pieces moved silently and obediently to their assigned place. Harry moved diagonally four squares to his right. Suddenly, Enid was swept off the board clean by the white queen. "Sorry about that, but I had to go out, it left you free to take that bishop over there, Hermione!" Hermione took Enid's cue and then the bishop in question. Soon enough, everyone except Harry, Ron, and Hermione had been swept off the board. Then, Ron realized something. "I've got to be taken out. It's the only way. It will free Harry to checkmate the king then we can go on," he explained. Ron made his move and was quickly swept off by the white queen. Harry then moved 3 spaces to his left to win the game.
In the next room was a troll, out completely cold, so there was nothing to do there. This was quickly followed by a riddle with potions. Maud quickly deduced that there were 7 potions, 3 of which were poisonous, 2 of which were actually beers in disguise, 1 would send them to the next room, and one would send them back to the chess game. Unfortunately, this meant that only one of the group could go on. In the end, Harry was chosen. Hermione went back to get help so, and no one wanted to drink any of the others lest they die right there. When Harry appeared in the next room, he was shocked at who he saw.