Following the events of The Last Colony, John Scalzi tells the story of the fight to maintain the unity of the human race.
The people of Earth now know that the human Colonial Union has kept them ignorant of the dangerous universe around them. For generations the CU had defended humanity against hostile aliens, deliberately keeping Earth an ignorant backwater and a source of military recruits. Now the CU's secrets are known to all. Other alien races have come on the scene and formed a new alliance against the Colonial Union called the Conclave. They have invited the people of Earth to join them. For a shaken and betrayed Earth, the choice isn't obvious or easy.
Against such possibilities, managing the survival of the Colonial Union will not be easy, either. It will take diplomatic finesse and political cunning: the "B-Team" advised by Lieutenant Harry Wilson.
As the story progresses, it deals with how humanity fares in a universe filled with other sentient races and without a military force to clash with them, since recruits from Earth stopped.