Twelve-year-old Julius and his nine-year-old sister, Mia, believe their grandfather's attic is just a dusty, boring room full of forgotten junk. But when a loose floorboard reveals a hidden metal box, they discover his strangest secret: a blueprint for a "Jötunheim Jump-Gate." Behind a towering, musty bookshelf, they find the device, and with one accidental touch, the familiar attic disappears. They are instantly thrown into a world of impossible cold. The air is sharp and clean, the ground is made of glittering blue sand, and a deep purple sky holds two silent moons. They have landed in Jötunheim, the land of the frost giants.

With their small portal home already tearing apart, they are found by Skadi, a kind giantess with snow-white hair. She promises to help them reach the main gate at the Palace of Endless Winter, their only other way home. But the journey is treacherous. They must survive a whispering blizzard that stings their faces, navigate glowing ice caves that echo with every sound, and outsmart a cackling frost sprite with a love for riddles. When they finally reach the palace, they discover the worst news of all: the gate is broken, its magical keystone stolen.

Stuck in a beautiful and dangerous world, Julius and Mia must race against time to find the keystone and get back to the attic... before they are trapped in Jötunheim forever.