Harry flung himself out from behind the bush and pulled out his wand.

"EXPECTO PATRONUM! " he yelled.

And out of the end of his wand burst, not a shapeless cloud of mist, but a blinding, dazzling, silver animal. He screwed up his eyes, trying to see what it was. It looked like a horse. It was galloping silently away from him, across the black surface of the lake. He saw it lower its head and charge at the swarming Dementors. . . . Now it was galloping around and around the black shapes on the ground, and the Dementors were falling back, scattering, retreating into the darkness. . . . They were gone.

Chapter 21