The Professor Wore Prussian Blue. Mysterious Devices, #6

Book six in the Mysterious Devices series of clockwork cozies set in the Magnificent Devices world!Family. Gold. Both precious. Both all too easy to lose . Daisy and Frederica Linden, having finally found their beloved father, Professor Rudolph Linden, are on the last leg of the journey they began so long ago. The only thing now in their way is the notorious gang of air pirates who haunt the archipelago between Port Townsend and Victoria. Corporal Kent of the Royal Canadian Airborne Police gallantly offers to escort their conveyance in an official airship, hoping against hope that Freddie will fly with him and give him an answer to a very important question. But Professor Linden's sense of propriety dictates that Daisy's fiancé William Barnicott and their ward Davey Fletcher should become the corporal's crew.
They gravely underestimate the pirates' abilities and are barely clear of the mainland when they are shot down. It is up to the Lindens to locate the pirate hideout among the islands and mount a rescue. But when Davey goes missing, will they find him in time . or is it the pirates who should fear one intrepid small boy?  "Prepare to be heartwarmed!" -License to Quill