Harry first meets Quirrell at the Leaky Cauldron, while being escorted by Hagrid to Diagon Alley to shop for school supplies. Quirrell is next seen at Hogwarts conversing with Snape at the start-of-term banquet, and then regularly while teaching Defence Against the Dark Arts lessons. During the school's Halloween banquet, Quirrell appears in the Great Hall to warn staff and students of a troll in the dungeons and then he faints, so he can freely make his way to the third-floor corridor where the Stone is hidden. Snape who, apparently, already suspected Quirrell was up to something, goes to the third floor in order to stop him. In later novels, the readers learn that Dumbledore had told Snape to keep an eye on the Defence Against the Dark Arts professor. Quirrell is unable to get to the Stone, but in the process, Snape is bitten by Fluffy. When Harry and his friends see that Snape has been bitten, they begin to suspect Snape is after the Stone for himself. While playing Quidditch, Harry is almost thrown off his broom by some sort of curse and he, Ron, and Hermione believe it is Snape who is responsible. They begin to suspect that Snape is trying to steal the Stone hidden in a secret chamber in Hogwarts; however, when Harry finally arrives in the chamber, he discovers that it is not Snape, but Quirrell, who is the real villain.