Graveyard Gods (The Raider and the Rapier #1) by Joseph Daniel, Bryan Arneson

SPFBO6

The currents sweep east, but the dead float south. This corpse laden tide carries with it the destinies of a tomb raider, a knight turned captain, and an empire fraying at the seams. A grave robber who dabbles in the alchemical arts, Edmond Mondego has spent the last seven years in search of a God Grave. He hopes to find magic within to relinquish his murdered wife's soul to the land of the living. What he finds instead is an imprisoned goddess stripped of her power but in full possession of divine secrets, including a rumor: every five years, one living soul is returned to the Emperor of the Gilded Islands. Meanwhile, the Lord Captain Augustin Mora, newly appointed commander of His Imperial Majesty's Ship Intrepid, guards the forbidden waters for his Emperor. Edmond's profane plundering of a God Grave and the machinations of the admiralty send Augustin on a quest to capture the tomb robber. But an enemy from his past muddies the waters, and Augustin is forced to reunite his old knight's guild and put hand to hilt once again. And so, Edmond sets every ounce of cunning and guile to raise himself through the ranks of nobility, evading Augustin Mora and all manner of assassins; he has only one goal—to convince the Emperor to use the magical boon for his wife's soul, and, failing that, to take the throne for himself.