In this ninth volume in the Motor Boys Series, The Motor boys in The Clouds , the boys have had very exciting and successful adventures on land and on the water, so a natural progression of their interests would turn to the skies. It is 1910, and while airships, that is, lighter-than-air aircraft had been under development since 1670, reliable commercial and military applications didn't occur until after 1900. The boys' airship, the Comet, is a combination airplane, with wings and engines, supported by a gas-filled balloon. Joined yet again by Professor Snodgrass and the Comet's designer and builder Rupert Glassford, they set off to win some flying prize money. Action in the skies!