Revolt Of The Galaxy: E.E. 'Doc' Smith

Book X of Family d'Alembert. The awesome forces of the Empire of Earth have destroyed most of the evil conspiracy's fleet, including the ship bearing the ice-blooded Lady A, when the Family d'Alembert uncover a plot on the planet Newforest, proving that the conspiracy commanded by the mysterious C is even more widespread than they have dreamed. For Yvette suddenly realises who - or what - C actually is, and she knows the terrifying true meaning of Lady A's boast that the conspiracy is the Empire!  the final book in this series.  Cover art by Stanislaw Fernandes.