Orchard (Gold) 2

After their mile-a-minute adventures on Virus Islands and fierce battle with the Sagittars on Colmen, twins, Starn and Esper Brock, are now returning home with their treasure to save Orchard Territory. But that’s proving to be very difficult as obstacle after obstacle get in their way: crash-landing their balloon, almost drowning in a lava bubble and learning the terrible truth about their father.
Sequel to Gold but can be read independently.