Two households, both alike in dignity,
In fair Verona, where we lay our scene,
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life.
Noah Coventry has walked through life knowing that his father, a Tempestarii
, murdered a family in an act of revenge. That was the same night he lost his older sister to suicide. It's never mentioned. Life has moved on as though nothing happened, and aside from that knowledge quietly haunting him, it doesn't see the light of day until his parents are killed in the most mundane way: a car accident.
He returns home and begins to settle his parents' estate. There, he learns more about what happened that night... and that YC survived, and was placed in foster care.
YC is, as an adult, in a position where s/he could use a bit of rescuing. (No victim personalities, though.) S/he has endured a difficult life, and is quick to accept an offer from a kind stranger: alone in an empty house, Noah Coventry reaches out, offering to take him/her on in an apprentice, and provide room, board, and a substantial paycheck in exchange for housekeeping services.
An apprentice of what? Magic, of course. He doesn't explain explicitly in the beginning, but his intent is to teach YC to control his/her latent gifts... and to do anything he can to atone for the sins of his father, which will gradually come to light.