The Legion of Space by Jack Williamson
Pocket Books, 1977 (Originally published 1947)
Price I paid: 75¢
They were the Legion, the small body of fighting men that had been chosen to defend the new democracy after the overthrow of the despotic interplanetary Empire.
Now, in the 30th century, an alien solar system is about to invade the human planets and the golden age ends abruptly in an outbreak of terror, suffering, and—worst of all—deadly treason that has allied itself with the dreaded monsters of Barnard’s Planet.
Sworn to protect mankind, John Star and his band of legionnaires must find AKKA, the mysterious weapon that guards the solar system, and rescue the beautiful young woman who keeps the weapon’s secret inscribed on her flesh. To succeed, they will have to brave the dangers of the sinister Medusa World, the black spider-ship, and the Belt of Peril where death and madness lurk.