A geas was a contract with the goddess of Fate. Sometimes one was born indentured, other times it was bestowed upon one as a curse. Because if one did not fulfill the terms of one's geas, one died. It was old magic, the magic of the gods, spoken in the tongues of those who controlled the dragons—and it was supposed to be extinct.

For what is magic, but passion freed from reason?

I cannot breathe, or see, nor swim,My darkness is composed of him.

Come closer, my dears, let me give you a warning,Of the fate that befalls those who stay out past morning,In the darkest hours before the dawn,When witches roam and demons spawn,And children die with spirit gone,Magicked away in the gloaming.

Everyone needs to escape sometimes, and retreating into somebody else's fantasy isn't nearly as satisfying as slipping into your own.