Cold as Ice: The Black Sisters

Aquila and Florence Black were an unlikely pair of sisters born to Alphard Black and Roma Black (nee' Lee). Where Aquila was dark and quiet, the more reserved older sister of the pair, Florence was lively and outspoken, always making sure everyone knew how she felt about everything.
Aquila graduated Hogwarts at the end of her sister's second year, elated to be Severus' first (and probably only) Potion's apprentice, and have the opportunity to stay near her little sister before she took over as head of the Black family. But Dumbledore has had other plans for the witch, it's not everyday you're offered the perfect weapon to dismantle a regime.
(This story starts from Philosophers stone (Florence's first year) until after the final battle. It will be mostly canon up until the Order of the Phoenix).