Covered by the Invisibility Cloak,

Covered by the Invisibility Cloak, Harry and his two friends go to the three-headed dog's chamber, where Harry sends the beast to sleep by playing a flute. After lifting the trap-door, they encounter a series of obstacles, each of which requires special skills possessed by one of the three, and one of which requires Ron to sacrifice himself in a game of wizard's chess. In the final room Harry, now alone, finds Quirrell rather than Snape. Quirrell admits that he let in the troll and that he tried to kill Harry during the first Quidditch match. Snape had been trying to protect Harry all along. Quirrell serves Voldemort and, after failing to steal the Philosopher's Stone from Gringotts, allowed his master to possess him in order to improve their chances of success. However, the only other object in the room is the Mirror of Erised, and Quirrell can see no sign of the Stone. At Voldemort's bidding, Quirrell forces Harry to stand in front of the Mirror. Harry feels the Stone drop into his pocket and tries to stall. Quirrell removes his turban, revealing the face of Voldemort on the back of his head. Voldemort/Quirrell tries to grab the Stone from Harry, but simply touching Harry causes Quirrell's flesh to burn. After further struggles, Harry passes out.