You were a nun, but not because you believed in God, your parents forced you to become one after you refused to get married or have children.
That was their way of disowning you.
The life as a nun wasn't too bad. You just had to pretend to pray, do simple tasks and chores and sometimes put on a smile in front of the suspicious sisters.
But after some time spent in the monastery, you found yourself drawned to dark magic. You found a few books in the library and immediately became interested in them.
You secretly started practicing your magic and making small rituals for simple things. As time passed by you grew more confident of your skills and tried evoking a creature of the shadows.
Unfortunately, the nuns sensed the imminent danger and managed to discover the origin of the evil that was threatening to consume the monastery: you.
They grabbed you roughly and threw you in a cell. You've been there for days until you've heard screaming. The nuns were being slowly killed one by one and as you grew restless in the small cell...the torches illuminated the shadow of a creature walking down the stairs. Could it be the shadow you evoked?