At Hogwarts, Harry meets his teachers, and becomes friends with Ron Weasley and Hermione Granger. The three of them accidentally find out that the potions master, Severus Snape, seems to plot on stealing something that is guarded by a three-headed dog. Since nobody would believe some first years to have found out such important things that even would incriminate a Hogwarts teacher, they take it on themselves to find out what Snape is up to. Their quest for the truth leads across many obstacles, from keeping up the everyday school life, a bewitched Quidditch match (Quidditch is a popular wizard sport), Fluffy, the three-headed monster dog and quite some tasks one has to overcome to get to the guarded object.