The False Knight of the Motorway by Arden Ellis

The world has been cursed by the gods. Their precious relics became poison long ago, and their cities radiate death. It is the dawn of a second Dark Age, if the priests and alchemists are to be believed. Ser Wright of Kenilworth doesn’t particularly care how or why the world was broken. Her only concern is regaining favor in the eyes of her lord—and if a menial errand to ransom her insufferable rival is the way to do that, Wright will grit her teeth and dutifully retrieve Ser Kai to face judgement.

But the simple errand forces Wright and Kai into a mission far more difficult: a quest for the legendary counteragent that could lift the curse once and for all. Wright’s duty is to retrieve it all costs, no matter who stands in her way—even if that someone is the sarcastic, dishonorable companion who Wright doesn’t hate as much as she thought.