To Fear the Light

In To Save the Sun Ben Bova and A. J. Austin told the epic tale of Adela de Montgarde, the brilliant astrophysicist who conceived the centuries-long plan to forestall the death of Earth's sun, thus preserving the original genetic material of the Empire of the Hundred Worlds - and of the Emperors who enabled her visionary plan.
Now, choosing to leave behind the man she loved, Adela has undergone cold sleep, returning two hundred years later to oversee the final stages of her project. She awakens to an Empire transformed: her son Eric is Emperor, faster-than-light travel has finally been achieved, and humanity has spilled out into innumerable self-sufficient new planets far beyond the Empire's Hundred Worlds.
More ominously, there are the alien Sarpans, bearing gifts of high technology. Are they as benevolent as they seem, or are they the threat the popular demagogue Jephthah claims they are? Several odd accidents add fuel to the flames fanned by Jephthah's rhetoric. To make matters worse, an investigation on a far planet suggests the existence of yet another alien race...