Imperial Stars — E.E. "Doc" Smith

The Empire of Earth, spanning more than a thousand solar systems, is threatened by a conspiracy from within. Now, with more than three-quarters of the Galaxy ready to fall into enemy hands, the Empire is forced to call on its top-secret weapon: the renowned Circus of the Galaxy featuring the d'Alembert family, a clan of circus performers with uncanny abilities. But even these super agents may not be in time to save the Empire.

The Imperial Stars is the first book in the "Family D'Alembert" series.