The Thirteenth Man by J.L. Doty
Approx. 117,650 words.
Published on February 4, 2012.
Charlie Cass returns from five years in a squalid POW camp to find the nine Dukes and the King conspiring against each other, and plotting with Charlie's old enemies. As interstellar war looms, he's forced to assume the mantle of the thirteenth Duke de Lunis, who, according to legend, is destined to fall beneath the headsman's ax. But if he can survive the headsman, all may fall before him.