The Consuming Fire by John Scalzi
In this science fiction novel, the sequel to a space opera series, an interstellar empire is on the brink of collapse due to the failure of the extradimensional Flow, the sole means of interstellar travel. As political intrigue and rebellion threaten to tear the empire apart, the emperox must confront internal and external enemies while seeking a way to save humanity from impending isolation and the subsequent downfall of civilization. With the help of a brilliant scientist and a cunning diplomat, the emperox navigates the treacherous political landscape, racing against time to uncover the secrets of the Flow before it's too late.