Magical touch
Sirius Black had wasted twelve years of his life. Twelve years that, as he just recently discovered, could have been a lot more eventful if he'd just appreciated the opportunity no other wizard was ever given.
The dementors knew he was innocent. They read thoughts like a gourmand reads the menu, daintily selecting joyful memories and brazen ideas. Sirius could attest, they would much rather feed on mass murderers than an unfortunate animagus. So much about their supposed support for that certain dark lord! They'd rather eat his soul, given a chance.
The large black dog touched his nose to Vaqqu's frost-lined sleeve, guiding the blind creature away from the steep stairs. Since Padfoot and the dementors had made their unspoken alliance, they often sneaked out of Azkaban together. Once a Marauder, always a Marauder.
But this wasn't just an unofficial leave from the isolated prison. Years ago, a young deatheater named Bartemius Crouch Junior had been convicted, but the one who had died in his cell had previously been radiating maternal love, then the corpse was soaked with polyjuice potion. Dementors were not so blind as to miss such poignant magic, but which wizard would consider their statement opposed to the influential Ministry official Bartemius Crouch Senior? Now their seeing-eye dog was more than eager to come along and investigate.
The outside world had changed a lot since the First Wizarding War, but they sniffed out Barty Crouch without difficulties. Who would have noticed them? Muggles only saw a shaggy stray dog, and turned a blind eye. Wizards and witches only saw the black robes of Azkaban's keepers, and, surprise, they turned a blind eye too. There was no difference.
They were still two hundred yards from the Crouch residence when Skipps gave a threatening howl, which the others soon joined. Their choir sounded like an especially malignant wind through the trees.
The wizarding world had lost so much with not appreciating the dementors' abilities, Sirius realized. He didn't need to ask what the howling was for: this was their usual reaction to an Unforgivable Curse.
He sneaked forward quietly, sometimes on two feet, sometimes on four. He had to see what Unforgivable act had happened to the pureblood family!
He heard a squeaky sound, perhaps that of a house-elf. He heard the rattling breath of the dementors, then their sated sigh. They had just breathed in some sort of very potent magic.
Suddenly, the door sprang open, and the younger Crouch was seen against the backlight, laughing like a maniac. He was holding his own father at wand point, rejoicing in his freedom now that the Imperius's effect was over. The next moment, the wand was pointed at a defenseless Sirius Black, who could have easily become the loose deatheater's first victim.
"Avada..."
Daire's hand touched Barty Crouch's wand, taking all magic potential from it. By the time the young man had said the second part of the curse, he was holding just a plain piece of wood.