On the frozen island of Skane, the sky speaks. Beautiful lights appear on clear nights, and their colours have meaning: Green means all is well, blue means a snowstorm is coming. And then there's red: Rare. A warning. Seventeen years ago the sky turned red just as Osa was born, unleashing a plague that claimed the lives of hundreds of villagers, including her own mother. This time around, can our heroine Osa prevent so many lives being lost again?