The posthumous papers of Rebecca MacKenzie document her adventures, along with her brother Doug, in 1920s China as the teenaged siblings are sent to live aboard their uncle's ship where they become involved in the dangerous activities of a mysterious secret society called the Honourable Guild of Specialists.

Siblings Becca and Doug discover important clues to their missing parents' expedition route and the location of Ur-Can, the fabled Storm City, and they embark on a perilous journey to the Takla Makan desert. They are racing against their Guild enemies by steam train, riverboat, and airship across the Himalayas, trying to save not only their parents, but the entire planet.