On Batuu, at the edges of the Unknown Regions, a threat to the Empire is taking root. It is troubling enough to warrant investigation by ruthless enforcer Lord Darth Vader and brilliant strategist Grand Admiral Thrawn. Fierce rivals for the emperor's favour, the formidable pair seem unlikely partners. Now they find themselves bound again for the planet where they once fought side by side. There they will be doubly challenged - by a test of their allegiance to the Empire and an enemy that threatens even their combined might.