Molly's daughter grows up in a world full of unicorns. She is, herself, a creature from a story, or so Molly guesses from how she cringes from iron and the mischief she causes. Molly wouldn't have left her to die out in the cold if she'd had green hair or pointed teeth.
Molly's one wish for her is granted before she turns eight.
Molly knows; she hears a child's giggles and the purrs of the unicorn she is bold enough to touch.
She's gone before Molly sees her, but she wonders. What other unicorn would come to little Amalthea Grue?