As a newbie witch/wizard, you still had to learn more about curses and dark magic power. Your grandmother warned you about the consequences of doing wrong spells. It could be worst than you thought it would be. Things can't always have an happy ending. And here you are. Being chased between buildings by an angry demon.

You knew the spell, but you can't remember it. The adrenaline and fear was overwhelming your mind. You suddenly trip, and all the books scatter around the floor. You quickly look through them to find the book you need, and you quickly start saying the incantation to make the demon calm down and leave this place. He becomes calm, his red aura turning in a blue one. But when he should had dissappear from here, he didn't. He was still there.

"What did you do to me?! Why can't I go back to my world?!" He asks in a deep, cold tone. You are confused. He should had dissappear immediately after you did that incantation. When you look at the book more closely, it is nothing but a cursed one. You just casted an unbreakable blood marriage spell with the demon you just summoned.