Children of the Lens by E.E. Smith

The Boskonian fleets defending Ploor were not all destroyed, of course. The vessels were inertialess. None of the phenomena accompanying the coming into being of the supernova were propagated at a velocity above that of light; a speed which to any spaceship is scarcely a crawl.

The survivors were, however, disorganized. They had lost their morale when Ploor was wiped out in such a spectacularly nerve-shattering fashion. Also, they had lost practically all of their High Command; for the Ploorans, instead of riding the ether as did Patrol commanders, remained in their supposedly secure headquarters and directed matters from afar. Mentor and his fellows had removed from this plane of existence the Eddorians who had been present in the flesh on Ploor. The Arisians had cut all communications between Eddore and the remnants of the Boskonian defensive force.