Narda stepped forward to investigate, but Julian stopped her. "No time now." It mattered little what manner of beast had waylaid them. The Jovian satellites, even frigid Callisto, had teemed with life of their own before colonization by Man. And, since the Terrans had preferred to build stupendous cities within transparent, berylo-plastic shields, shaped like bottles, there had been small point in the systematic destruction of native fauna. The cities were largely self-sustaining, anyway. All commerce and intercourse was carried on by air. Only adventurers and fools would venture into the wastelands ... adventurers and fools, and perhaps, members of the _Dekka_. As they reached the base of the cliff, Julian glanced back at Narda and smiled. "Be alert, I'm forcing issues tonight ... inaction's killing me!" He was like a Martian eagle--poised for battle. Narda sensing his mood smiled thinly in the shadows. She wondered silently what new, macabre mission would be assigned to them this time. And hoped that the summons meant something far more than the usual battle between rival Societies striving to milk the venom from each other's fangs. For on at least three major Moons, Io, Europa and Callisto, men and women were struck by an invisible foe that left them trembling with fever, and when that dwindled away, a tide of silver rose from the roots of their hair, and even the eyes became luminous with the deadly patina. Nothing was known of Ganymede. It was hard to tell in the absence of reports, for Ganymede, aside from its own native civilization, had been colonized by Terran Mutants, who could and did procreate, thus perpetuating their race. But the victims of the Silver Plague were left sterile. It was hard to differentiate. Meanwhile the Moons were dying! And yet, a stubborn feeling in her heart kept insisting that perhaps the _Plague_ was something man-made, and like all poisons should have an antidote. She glanced at Julian and shuddered with anguish--there would be no progeny for them--her own turn might be next! What a fiendish weapon, if _it was a weapon_, she thought. The ultimate in refinement of warfare--a refinement that in their Moons had been going on for three hundred years! * * * * *