Ten-year-old Siri and her little sister Miki live with their elderly father in an Arctic archipelago. One day, while they are out gathering snowberries, Miki is abducted by Captain Whitehead, a notorious pirate, who is rumoured to enslave the children he steals in a diamond mine. To prevent her father from risking his life to find Miki, Siri sets out to find her sister herself. In Siri s adventure on the seas she will encounter wolves, sailors and mermaids, profound evil and true humanity.