In pursuit of stolen treasure in 1865 Ireland, thirteen-year-old Ailish winds up trapped on the Great Eastern as it sails The largest ship ever built, the Great Eastern's mission is to lay the fi rst undersea telegraph cable across the Atlantic Ocean. On the journey, Ailish gets help from a young boy, Davy, who seems to live belowdecks. She makes friends with an Irish sailor and tries to track down the hiding place of her father's treasure. The crew must battle the seas and the mishaps of their cable-laying mission, some of which would appear to be sabotage. Through many adventures, Davy is her constant companion. But why won't he ever come topside? Can Ailish use her wits, her determination and her friendships to survive the trip, let alone save the day?