A silvery wisp of vapour shot from the tip of the wand and the Dementor slowed, but the spell hadn’t worked properly; tripping over his own feet, Harry retreated further as the Dementor bore down upon him, panic fogging his brain—concentrate—
A pair of grey, slimy, scabbed hands slid from inside the Dementor’s robes, reaching for him. A rushing noise filled Harry’s ears.
“Expecto patronum!”
His voice sounded dim and distant. Another wisp of silver smoke, feebler than the last, drifted from the wand—he couldn’t do it any more, he couldn’t work the spell.
There was laughter inside his own head, shrill, high-pitched laughter… he could smell the Dementor’s putrid, death-cold breath filling his own lungs, drowning him—think… something happy…
But there was no happiness in him… the Dementor’s icy fingers were closing on his throat—the high-pitched laughter was growing louder and louder, and a voice spoke inside his head: “Bow to death, Harry… it might even be painless… I would not know… I have never died…”
He was never going to see Ron and Hermione again—
And their faces burst clearly into his mind as he fought for breath.
“EXPECTO PATRONUM!”
An enormous silver stag erupted from the tip of Harry’s wand; its antlers caught the Dementor in the place where the heart should have been; it was thrown backwards, weightless as darkness, and as the stag charged, the Dementor swooped away, bat-like and defeated.
“THIS WAY!” Harry shouted at the stag. Wheeling around, he sprinted down the alleyway, holding the lit wand aloft. “DUDLEY? DUDLEY!”
He had run barely a dozen steps when he reached them: Dudley was curled up on the ground, his arms clamped over his face. A second Dementor was crouching low over him, gripping his wrists in its slimy hands, prising them slowly almost lovingly apart, lowering its hooded head towards Dudley’s face as though about to kiss him.
“GET IT!” Harry bellowed, and with a rushing, roaring sound, the silver stag he had conjured came galloping past him. The Dementor’s eyeless face was barely an inch from Dudley’s when the silver antlers caught it; the thing was thrown up into the air and, like its fellow, it soared away and was absorbed into the darkness; the stag cantered to the end of the alleyway and dissolved into silver mist.
Moon, stars and streetlamps burst back into life. A warm breeze swept the alleyway. Trees rustled in neighbouring gardens and the mundane rumble of cars in Magnolia Crescent filled the air again.
Harry stood quite still, all his senses vibrating, taking in the abrupt return to normality. After a moment, he became aware that his T-shirt was sticking to him; he was drenched in sweat.