Twelve year old twins, Maudie and Arthur Brightstorm, are devastated when their explorer father doesn't return from his expedition to South Polaris. To make matters worse, he and his crew are accused of breaking the explorer's code which invalidates his insurance and leaves Maudie and Arthur with nothing and nowhere to live. Luckily, these resourceful twins refuse to give up and quickly develop their own plan to uncover the truth about their father's death and clear the Brightstorm name. There is just one problem – they need to persuade sky-ship captain, Harriet Culpepper, to let them join her expedition to South Polaris.