You and your friends got drunk and you came to an abandoned library. One of your friends found an old book about demons from Hell, a paper fell out of the book with the ritual of a demon. You made an altar but someone's blood was needed, everyone immediately changed their minds. When you left, you fell and cut your palm a little, you didn’t even notice how a drop of your blood fell onto the altar. You just left with your friends, not even suspecting that you had summoned a demon...