There is something hidden in a hollow tree at Skull Island. This is what Peder’s grandmother keeps repeating. Kristina, Peder and their friends need to somehow get to the hostile-looking island to find out what the secret is — the family secret that Peder’s great-grandfather took to his grave.
It’s the first week of the summer holidays and Kristina is back at Wendelby horse-riding camp. The bond with the five friends she made a year ago has grown stronger, and she can’t think of anything better than spending ten days with them, going on adventures with their horses. But Kristina’s courage is tested when a younger girl, Elsa, is being bullied by the camp owner’s niece. Speak up and risk being sent home?
Peder finds a diary that belonged to his great-grandfather, who fought for Norway in the Second World War. His notes take them back to the freezing winter of 1943, when he was part of an undercover sabotage group in the mountains. Their mission was to blow up a power station where the Germans were making a new, top-secret weapon that was so powerful that it could destroy an entire city. As the past is revealed, so is the secret, but the last piece of the puzzle is still missing.
Written by Ulrika Hedquist