As long as you could remember, you were called Jack Spades, probably because of the spades-shaped brand on your hand that let you sense magic. You have no idea why someone would have branded a baby with such a thing, and even less idea why they would abandon them. Growing up, you were raised by Mother Cat, a criminal who lead a band of urchin thieves. With your unique skills, she often sent you to steal magical artifacts and books. (She was not the sort to be concerned with the safety of her charges) Sometimes she even let you read a few of them, though your grasp on magic was... dubious at best.
Mother Cat said that you would rise to greatness one day, provided you don't get yourself killed first. Personally, you didn't really care about achieving greatness or anything like that. You're perfectly alright with anything.
Little did you know that your life would change so much, when one day Mother Cat charged you with gathering information on a certain mage. She had been asking around in discreet circles for thieves with magical knowledge, and talking about a strange sort of prophecy of a figure called the 'Spellthief.' Never one to pass on an opportunity for profit, Mother Cat had given you a chance to work with the mage, provided that you figure out whether or not the deal is a trap.
You have been given a chance to impress Mother Cat, though you aren't sure on the details. Maybe some old-fashioned burgling was in order, or some magic trickery, or other forms of shenanigans.