Madsi has always loved the stories that her clever, strong-willed sister, Lisbet, told her late at night in their cabin. Madsi never expected Lisbet to become one of those tales. But last year, her sister disappeared in the night, snatched away by the Northern Lights.

This year when the Lights appear in the sky, Madsi begs them to free her sister--and a girl falls to earth right in front of her. But it's not Lisbet. This girl's name is Torin, and she demands that Madsi take her to a witch who can put her back into the Lights, where she went by choice. Madsi doesn't know what to believe--but if she takes Torin to the witch's mountain, maybe she can get Lisbet back. They set off, joined by Espen, an annoying (but surprisingly helpful) boy from Madsi's village.

Madsi has never thought of herself as brave, but as they endure the wilds and face monsters she's only heard about in tales, she finds unexpected strength. Can she also find the truth of what happened to her sister?