With the strange plans for an even stranger machine in his possession, along with a coded message from a long-dead castaway that could be the key to unlocking its secrets, Gerald finds himself at the centre of a web of mystery and danger. Masked gunmen have taken over his luxury yacht. His parents have been kidnapped. And one of his closest friends has betrayed him. His old enemy Sir Mason Green seems to be pulling all the strings. Or is he? Gerald, Ruby, Sam and Felicity take off on their final exciting adventure, from glaciers to jungles and the depths of the Pacific Ocean to an island teeming with the most bizarre creatures on earth.