Callisto to the RescueAll humanity of Callisto, the fourth major satellite of Jupiter, had for many years been waging a desperate and apparently hopeless defense against invading hordes of six-limbed beings. Every city and town had long since been reduced to level fields of lava by the rays of the invaders. Every building and every trace of human civilization had long since disappeared from the surface of the satellite. Far below the surface lay the city of Zbardk, the largest of the few remaining strongholds of the human race. At one portal of the city a torpedo-shaped, stubby-winged rocket plane rested in the carriage of a catapult. Near it the captain addressed briefly the six men normally composing his crew.
"Men, you already know that our cruise today is not an ordinary patrol. We ar
