Siblings Art and Myrtle Mumby are back in a third adventure (after Larklight and Starcross) set in a space-aged Victorian adventure (think Steampunk) that further explores the history of their mother. It all starts on Christmas Day in 1851, and the whole family is settling down for dinner when they are visited by the crew of the Sophronia. The ship's captain, Jack Havock, and his crew are friends that have joined the Mumbys on their earlier adventures.

During the course of the holiday's festive reunion, the Mumby's receive word that an old friend and his daughter disappeared in orbit around Uranus. The only thing anyone knows is that he sent out some sort of message just as their ship was disappearing. No one knows whether it is a warning or an S.O.S. The Mumbys quickly head off on a massive British battleship toward Uranus, or the more polite Georgium Sidus, where the path to the Reverend Cruet and his daughter Charity ends and the journey full of adventure, humor, and mystery begins.

Superbeings, massive moths, and space battles that are offset by snarky comments made by Art and Myrtle about each other and those around them throughout the book show that this is a great addition to a series that is really popular among both boys and girls. The tales capture the tone of Jules Verne and H.G. Wells along with Lemony Snicket.