Three friends - Julie, Mette and Naisha - are enjoying the first snow in the village. They have snowball fights with the boys and look forward to Christmas. One day Naisha suddenly disappears. With a secret address written in invisible ink as their only clue, they sneak onto the night train to the city. They need to find Naisha before the police do.

The curious Nora, Simen and Lars decide to start the hunt for the sacred Olav shrine in or around the medieval church Nidaros Dome, which has been gone for hundred of years. But they are not the only ones interested in finding the treasure.