Ganymede is the fourth book in Cherie Priest's Clockwork Century series, following Boneshaker, Dreadnought, and Clementine. While the first book took place in and around a ruined Seattle, filled with poisoned air and zombies, and the second book followed the journey of Civil War nurse Mercy Lynch as she travels across the country, avoiding attacks from both soldiers and zombies, Ganymede takes place primarily in New Orleans. Characters from earlier books make cameo appearances, including Briar Wilkes and Mercy Lynch, but Ganymede is very much a distinct novel set within Priest's Steampunk universe.
The interminable Civil War keeps dragging on, and the independent republic of Texas, while nominally neutral between South and North, has taken control of New Orleans. Josie Early, a black woman who runs a brothel in the Big Easy, contacts Andan Cly, an airship pilot in Seattle and former lover, for a lucrative but dangerous job: extracting a Confederate submersible from under Lake Pontchartrain and delivering the ship to a waiting Union warship in the Gulf of Mexico. Earlier efforts to steer the Ganymede have cost many lives; Josie hopes that an airship pilot would be better-skilled to operate the submersible than someone whose skills are on surface ships.
Providing a thorn in the side of the Texians are the pirates, whose base in Barataria dates from the time of Jean Lafitte. When two Texian officers go missing, the Texians take the opportunity to clear out the pirates' base of operation.
In addition to the danger from both the Texians and the Confederates, Josie must contend with the growing danger from the zombie population of New Orleans. She connects the zombies with sap, the drug that has become increasingly popular, though she is unaware that sap is made from the poisonous gas in Seattle.
Although this novel stands alone from the others in the Clockwork Century series, sap is clearly part of the connective tissue among the three books. I presume that this will be resolved in a future book in the series.
Priest knows how to draw interesting characters: Josie herself, operating a shadowy business despite the twin handicaps of being a black woman in the 19th century South; Ruthie, one of Josie's "girls," with a secret of her own; and Andan, a former sap runner who wants to go straight and fly legitimate cargo, but who is drawn back to New Orleans in large part because of Josie. New Orleans is almost a character in its own right, a place of intrigue, of voodoo, of oppressive humidity and uninhibited behavior. I found the story in Ganymede to be a more interesting one than that of Dreadnought (even though Mercy Lynch is another intriguing character), and look forward to the next book in the series, The Inexplicables (which just came out), which returns the series to Seattle.