Her fingers wove around the steely cold of the prison bars, gripping them tightly, furiously. She stood staring, invulnerable to the cold of the dementors, welcoming them to feast upon her nothingness, for she had grown cold to her pain over the years...

Sophie gave a start as a gust of wind came from behind her and the door creaked open. She whirled about, eyes narrowed and scanning the Entrance Hall, but there was no one in sight. She stepped forward and closed the door firmly behind her. 
Someone had been there. She had sensed it, she had heard the ragged breathing, as if the person had been running. Whether by the concealment of what had to have been very Dark magic, or the offhand chance that the intruder owned an Invisibility Cloak, someone had slipped into the castle and Sophie had been the only one to notice.

“Did you hear something?” Harry asked.  “Upstairs, quickly!”
Harry and Sirius sprung into action at the sound of the strangled yell that drifted from the second floor; they took the stairs two at a time, four bare feet padding softly upon the cold wood of the floor.

The intruder was already standing over Eli's bed, wand drawn and one hand over his mouth to stifle any further noise.