Tonks fell through the door, wand at the ready, into the deserted street. Rows of decrepit garages lined a cobbled alley lit by a single, rather pathetic lamppost. The two Death Eaters they had been pursuing had vanished. She swore under her breath; they'd almost had them. As she stepped out into the alley she shivered. Something felt wrong. There was an ugly chill to the air, like fog, although the sky was clear. Even for the small hours of the morning, it was too cold for late July. She turned to Lupin, who lingered by the doorway through which they'd just come.
"We've lost them." she sighed.
He stepped out to join her.
"Hang on a minute…" then he fell silent, face raised to the night air, like he was trying to listen, or was it something else. Tonks wondered for a moment if werewolves could track scents, or if that was just mythology. "This way", and he started off towards the darker end of the alley.
"How do you know?" Tonks demanded.
"I've just got a feeling. Not a good feeling, mind."
Lupin, Mr Rational, acting on a hunch? Tonks was surprised, but under circumstances it was the best lead they had, so she supposed she would have to go along with it.

At the end of the alley there was a sharp turn into a driveway that lead towards the main street. As they rounded the corner, the sight that met them froze Tonks to the spot. Prostate on the ground lay a fallen Death Eater, the mask pulled back from his bearded face, frozen in horror. Over him hovered a mass of black, a humanoid form in a cloak of ragged, pitchy gauze that twisted in some unfelt wind. The creature's hooded head was transfixed above the fallen man's open mouth, from which a small but infinitely bright ball of light painfully slowly drifted upwards. Then Tonks did something she never thought she would ever do on duty. She screamed.

The scream split the night, breaking the creature's rapture. It raised itself, turned, and faced them, extending a hand, grey and rotten looking.
"Run!"
Lupin had grabbed her arm and was dragging her away from the scene, back down the alleyway. Tonks ran. She didn't know where, just that she had to get away from that thing, she blindly followed Lupin. A brickwork maze of dark back alleys, passageways and footpaths unfolded around her, the air unnaturally thick in her lungs. They vaulted a low wall, and crouched behind it.

"Tonks. Nymphadora. Look at me." Her eyes met Lupin's. He was breathing hard, his face bloodless. "This may sound counter-intuitive, but you have to calm down. Those things feed on emotion, the more scared we are, the easier we are for it to track. Moreover," he swallowed and glanced over his shoulder, "we're not going to outrun it. We need to apparate away from here, and we can't do that if we're panicking. So, deep breaths…" he held her gaze. "Ready?" She nodded, and they got to their feet. Too late, the creature was already upon them. It floated above the wall like some vile bird of prey. Tonks suddenly felt so lonely, so small, every mistake, every inadvertantly hurtful word she'd ever said twisting up her insides and draining the blood from her head. At her side, she heard Lupin murmur something, but the words didn't register. A graceful silvery form flew from his wand towards their assailant. And then, for the second time that night, Nymphadora Tonks did something she never thought she would ever do on duty. She fainted.