Harry backed away from the Dementor, stumbling over the hem of his robes. It advanced towards him, turning its head towards him taking in a deep rattling breath. Harry immediately felt the coldness wash out of him and every happy thought rush out of his body to be replaced with his many unhappy ones. His parents dying, Sirius falling through the veil, Cedric being murdered in cold blood, Umbridge's 'detentions'. Harry tripped over a branch and fell hard on his back, the wind getting knocked out of him. The Dementor hovered over him and slowly drew down it's hood. Harry's breath caught in his throat as he saw the gaping hole and the rotted, scabbed skin, he immediately groped for his wand and immediately began to dig in his memory for a happy memory.
'Expecto Patronum!'
The silvery stag erupted from the end of Harry's wand and chased away the Dementor. It was funny really; the memory was one of him having a snow ball fight with Ron and Hermione. Harry felt warmth slowly seep into his frozen body again as the Dementor fled, the stag turned back and gently trotted back to Harry, fading into the air as it returned. Harry staggered sideways into the alley wall as feeling returned to his jelly-like legs.
'Harry!' Hermione's concerned voice drifted over the wind. Her worried face swam into his sight, making him smile. 'Are you okay?'
'I am now. Thanks Hermione. You saved my life.'
Harry walked slowly away leaving a confused Hermione behind him.