Cloud Rider

Rold Simms and his sister Tyler are caught between the warring Scientists and Industrialists faction when Tyler is accused of a planting a bomb on a space transport. They escape to the frontier planet of Salkinia where they get separated. Rold falls in with the native Tetons while Tyler is held captive by a marsupial race of mercenaries working for the Industrialists. Their fate, as well as the fate of human civilization, depends on the capricious Living Clouds, which inhabit Salkinia -- and to the mysterious Teton woman who is the last Cloud Rider.