In 1981, the British wizarding world is at war. The Dark Lord Voldemort, He-Who-Must-Not-Be-Named, is terrorizing the country at the head of a band of purity-mad followers. People who oppose him are disappearing left and right, and nobody is sure who to trust. Lily and James Potter are two of the best fighters left standing against him. On the advice of their friend and comrade-in-arms, Albus Dumbledore, they turn their home into a secret base, where they hope they and their infant child, Bruce, will be safe from any attack.
On Halloween night, all their hopes prove false. Voldemort himself arrives at Godric's Hollow, kills Lily and James, and then turns his wand on the child. No firsthand accounts survive of what happens there, but the dark wizard vanishes from the face of Britain, and Bruce is found alive in the ruins, unharmed except for a scar on his forehead in the shape of a bolt of lightning.
To hide him both from those who wish him ill and those who wish him well, Dumbledore places the newly orphaned baby with his muggle aunt and uncle. Thus do ten years pass, and for most witches and wizards they go well--for most, but not for all.