The Clockwork Caterpilar. Red Sabre, #1

Athemisa is a continent divided. To the east lies the industrialists of the Thyrian Empire. To the west lies the Jader colonists of the Celestial Throne. Scarred wilderness separates them with a slew of railways vying for the services of the new world's inhabitants. In Athemisa, the rails mean everything. They are the lifeblood of the remote settlements reliant on shipments of food and supplies. They are the land claims staked by foreign thrones measured by troop movements and weapon deliveries.
For Felicity Metticia, they are a way of life. Felicity is a rail mercenary, making a living on the wild frontiers by running contracts between the two empires. Life is difficult, but she has a crew of her own as capable as it is diverse. Schroeder, her right hand, is a wealthy rail magnate's son disowned for his unprincipled lifestyle. Pacal is her fearsome crackshot, hailing from the recently unshackled south.
A haunted war surgeon, rescued Jader girl, righteous navigator and reclusive engineer keep her train on the rails. They have managed many difficult jobs. But when the bounty posted by the magnate Bernhard Nikolai becomes more trouble than it's worth, Felicity must follow-up a dangerous proposition from old connections in order to keep her crew paid and her engine running. Unfortunately, many dangers await her on the tracks.
Pirates strike from armoured engines. Revolutionaries wield their idealism like a weapon without concern for friend or foe. And always the Thyrian magnates seek to control who can and cannot ride their rails. Torn between a big pay-off, past obligations and her principles, Felicity must navigate the troubles to find a mechanical wonder whose humble exterior belies its ability to reshape the face of the world.