Harry snapped awake at midnight, something shifting in his perception.
He had always been susceptible and thus sensitive to Dementors, and studying Dumbledore's ideas and ways had increased that. The sudden increase of them here and now made his senses scream, even in sleep. As he snapped up to a sitting position in bed, fully awake, he knew, somehow, that there were more Dementors, almost double what there had been.
He was out of bed and running, wand in hand before he even thought it out.
His daughter was out there. Harry had never been a man to run from danger, and whether it was bravery or stupidity, this trait had only increased with the birth of his children. He had thrown himself in the line of danger for strangers, for a nation, for friends, and he would do the same for his daughter, schedule be damned! He received the text from Dave a moment later, and swore at the confirmation of his worst fears.
As he ran, he was punching buttons on his phone and pushing out an urgent text.
He flicked his wand down himself and whispered a word and his speed doubled, and doubled again and he blurred down the stairs, running with every ounce of a Auror's strength, a father's love, and a hero's heart.
When he burst out of the hotel, and ran for where they were, he was already summoning his happiest memories, girding himself for the coming fight. Images of Lily Luna's birth, seeing his mother again here and talking to her, seeing his father alive, and Sirius too, and even of the first bloom of Ginny's and his love, all flickered into his mind and he felt warmth roll through him, dispelling fear and pain.
A moment later, he saw the Dementors, around a fallen Lily, and Dave defending her and he waited no longer. With a voice practiced and honed, he shouted the spell as his wand snapped down.
"Expecto Patronum!" Radiance burst out of his wand, a vibrant sun of light in the darkness that pushed it back, and a moment later a stag ran through the air toward the Dementors, head lowered and horns high. It slammed into them like a Muggle locomotive, and hurled itself about, making a mockery of their organization.
It grew brighter yet as he poured all of his good feeling, all of that good memory of Lily Luna at his side, into it, and the Dementors were forced back, and back, and back again. At last, unable to face the form and power he was putting into it, they turned and fled, and Harry felt his cheer rising as they moved away.