Cherie Priest's Clockwork Century series of steampunk novels expands into another dimension -- under the sea -- in her latest book, Ganymede.

It's the late 1880s, and the Civil War still rages. Some folks are desperate to see the conflict end. Josephine Early, a brothel operator and Union sympathizer in New Orleans, wants to see a piece of stolen Rebel technology -- a functional submarine -- get into Northern hands, but it's not the Confederate army and navy that stand in her way. New Orleans is an occupied city, controlled by the independent Republic of Texas, and getting the prototype sub from its hiding place on the floor of Lake Pontchartrain out to a waiting federal carrier in the Gulf of Mexico will be no easy task.

Oh, and there are zombies -- or, rather, zombis -- too, roving along the waterfront and making life particularly difficult for anyone who ventures there.

Sailors seem unable to pilot the new underwater technology without drowning. With its creators dead or in prison, Josephine turns to the sky: dirigible captain Andan Cly, a semi-reformed air pirate living in the walled, underground city of Seattle, might still owe her a favor -- or be lured by lucrative pay -- enough to tackle the job.

This is the third official novel from Tor in the Clockwork Century series, following Boneshaker and Dreadnought; an unofficial book in the series, Clementine, was published by Subterranean Press.

Each book introduces new characters, expands on supporting roles from previous novels and shifts former protagonists into the background. It's a compelling technique that grows Priest's active cast without risk of becoming stale -- and she's handy enough with her characterizations that no one ever seems like a retread of old heroes, flawed or otherwise.

The action, too, stays fresh. Priest has an inventive eye when it comes to the stylized technology of her American steampunk world, putting readers right in the belly of the beast where they can hear the faint hiss of gas escaping a copper joint, the sputter of chancy electrical wiring, the drip-drip of water condensing inside her fledgling Ganymede as it crosses the sultry bayou.

I loved this book and I love this series. Josephine predicts the submarine technology will bring a swift end to the long-running war. I hope not, because Priest's Clockwork Century is just too durned good to end.