Year of the reaper / Makiia Lucier.

Before an ambush by enemy soldiers, Lord Cassia was an engineer's apprentice on a mission entrusted by the king. When plague sweeps over the land, devastating the kingdom, even Cas's title cannot save him from a rotting prison cell and a merciless sickness. Three years later he wants only to return to his home in the mountains and forget past horrors. But his castle has become a refuge for the royal court... and they have brought their enemies with them. When an assassin targets those closest to the queen, Cas forms an unexpected bond with a young historian named Lena. Searching for the "why" of the attacks, the discover a secret that could plunge the kingdom it back into war. -- adapted from jacket