Disclaimer: I do not own Harry Potter.
By Silver Sailor Ganymede
When Regulus saw the massive, bear-like black dog in the garden of number 12, Grimmauld Place he was quite convinced that it was a Grim. It was terrifying, but it wasn't that much of a surprise, really; the area had got its name from the fact that great-great-great uncle Sirius had seen a Grim there shortly after the last building was finished and died within forty-eight hours. This, of course, was long before the muggle scum had swarmed in even on this once prestigious part of London.
Still, Regulus hoped that it wasn't a Grim. No matter how awful the summer holidays had been so far, he didn't really want to die. Sometimes he wanted mother to die (she and her constant rants on blood-purity). Sometimes he wanted father to die (he and his efforts to 'persuade' of Regulus to go and join the Dark Lord. Regulus would go when he was ready, when he was of age, but not before that). Sometimes he even wanted Sirius to die (but only when Sirius decided to remind him how much of a coward he was for chosing to become a Slytherin like every other Black in history). But he certainly did not want to die himself.
It was about two-o-clock in the morning when he saw the Grim. The night was black as pitch already, so all he could really make out at first were the creature's gleaming white eyes. He cast a lumos spell so as to get a better look at it, and paled in horror as he saw the vast, black dog standing there, a denizen sent from Hell to take him away.
The Grim snarled at him, then turned away. Regulus felt sick. Then he saw the dog pick up a bundle in its mouth (the body of a child it had killed, perhaps? Or maybe just something equally macabre) and jump over the wall.
Regulus shook his head. Surely he was just seeing things, surely! After all, everyone knew how insane great-great-great uncle Sirius had been; why, he even made cousin Bellatrix look normal. He got back into bed, barely noticing the momentary roaring of engines and flashing of lights across the sky.
It was only the next morning when he saw that his brother's name had been scorched off the family tree that Regulus had an inkling of what the Grim had really been.