The Mysterious Recorder and the Door to Elsewhere - Michael Davies

Alex finds a beautiful recorder hidden in his house and when he plays it, a door to another world opens. He and his friend Kate travel in a strange world, meeting monsters and people who have been there for many years. Some of the adventures are sad, meeting a squad of Australian soldiers who have been for some years but they don't know who the enemy is or how they got there. Some are frightening and they also find there is a mystery about their own parents that they can now resolve.