A Key Called Promise (джен)

Slytherin has been lumbered with a disagreeable, low-class, shouty, raggedy little troll. With more pride than self-preservation. Ick. And he's even half muggle! Or maybe just half mother-hen... But either way, noisy, and trouble, and... an excellent decoy, actually, and oi, Snape, what do you want for your History notes?
Or: the darkest baby Death Eaters in Slytherin find each other so consumingly alien they forget to grow up hateful.