Colin Creevey
The scream summoned Colin like a beacon. He loped up the last flight of stairs toward what he was now sure was his brother's cry. He had no idea how he knew the high-pitched shriek following the taunt was Dennis, but he felt it in his gut.
Colin rounded the corner and saw the back of the Death Eater standing over a body that was bleeding madly from one shoulder. His face drained: Dennis was curling into a fetal position holding an arm that looked as though it weren't attached to his body. Colin had to help, he simply had to.