Strange and frightening things happen at the school. First, Sasha is kidnapped off the school bus during an outing, but then mysteriously freed and left by the road within hours. Then Wendy is kidnapped from the school building at night, but she is not freed. Instead, a ransom note is sent to the school, demanding the silver locket that she normally wears. What is the secret of Wendy's locket? Who is behind the kidnappings and why is Alex's father, a colonel in the Australian Army Military Intelligence involved in the case? Sasha, Wendy, Alex and Sally must all show great courage and determination to help solve the case and avoid the serious dangers presented by the mysterious people behind the events.