Young Harry Potter (Daniel Radcliffe) has to lead a hard life: His parents have died in a car crash when he was still a baby, and he is being brought up by his Uncle Vernon (Richard Griffiths) and Aunt Petunia (Fiona Shaw). For some reason unbeknownst to the bespectacled ten-year-old, the Dursleys let him live in the small chamber under the stairs, and treat him more like vermin than like a family member. His fat cousin Dudley Harry Melling), the Dursley's real son, keeps bothering Harry all the time. On his eleventh birthday, Harry Potter finally receives a mysterious letter from a certain Hogwarts School of Witchcraft and Wizardry, telling him that he is chosen as one of the future students of that supposedly renowned school. Hagrid (Robbie Coltrane), the gigantic man who brought the letter, finally introduces Harry into the real circumstances of his life: His parents were a wizard and a witch, they were killed by the evil wizard Voldemort (Richard Bremmer) protecting him. Harry still has a lightning-shaped scar on his forehead from that event. Since he survived the attack as a baby, and also somehow deprived Voldemort from his powers, he has been famous in the wizarding world ever since. The Dursleys, strong disbelievers in that magical crap, never told Harry anything about his true self. So, Harry is strongly surprised, yet absolutely happy to start his training. At Hogwarts, Harry meets his teachers, and becomes friends with Ron Weasley (Rupert Grint) and Hermione Granger (Emma Watson). The three of them accidentally find out that the potions master, Severus Snape (Alan Rickman), 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.