The expedition led by Rick Carter won successive victories in the depths of the universe and formed a "Sentinel Alliance" with aliens who rebelled against the Invid. But in 2031, the earth was occupied by the Invid led by Regis. In 2044, the Expeditionary Force changed direction and began to march towards the ancient home of mankind, the earth. With the help of Sentinel Alliance member Haydn, General Edwards equipped the fleet with Shadow Technology, which protected the fleet from Invid detection equipment. In addition, the Expeditionary Force relied on the Haydonites to develop more powerful neutron S missiles. Half the planet was sacrificed in order to drive the Invid out of the earth. In the meantime, SDF-3 mysteriously disappeared, and Rick discovered something strange about the neutron S missile. He warned the Expeditionary Force against using this deadly weapon. But the expedition has launched a final attack on the Invid...
