"What?" This was Steve, more than slightly incredulous. "Anthrovacs are mild creatures and unless they're attacked they won't do anything violent." "That's what I thought, Stedman. I don't know what to think now. The anthrovacs escaped--and freed all the other animals. We've been out longer than the _Gordak_, we have a couple of dozen prize specimens. Lead by the anthrovacs, they've taken over the ship." "Now you're joking," Teejay told him. "They're all brainless, those creatures, except for the anthrovacs." "They _were_ brainless, Captain Moore. But not now. Now they behave logically, with a purpose, and they've taken over the _Frank Buck_ from stem to stern--all except those animals that need a special sort of atmosphere to breathe, and they've remained in their bubbles. "Otherwise, the animals took over. And I suppose you can imagine--the crew was too astounded to resist, especially since the anthrovacs had gotten hold of neutron guns and seemed to know how to use them. Result--we've all been disarmed, we're prisoners aboard our own ship, and bound for I don't know where." "Sounds crazy to me," Teejay said, and stalked toward the door. Steve took a quick step after her, but Barling held him back. "Let her find out for herself, Stedman. Then maybe we can talk sense." Teejay opened the door, stepped out into the corridor. Tensely, Steve waited, ready to bolt after her at the first indications of trouble. But what he heard was a yelp of surprise from the woman, and then she came running back into the lounge, slamming the door behind her. "A Martian desert cat!" she cried. "It didn't do anything; it just stood there, all ten feet of it, looking at me!" "Then you believe me?" Barling demanded. "As I see it, we must have been struck by some cosmic radiation which mutated the animals, and--" "No," Steve told him bluntly. "That's impossible. First place, any such change would have to be selective. _All_ the animals wouldn't be affected. And more important, mutation takes generations to manifest itself. You never see the change at all in the original creature. Look at Earth, way back in the early years of atomics. Genes were mutated at those two island cities--Nagasaki and, umm-mm, I forget the name of the other. Anyway, genes were mutated, but it took over two hundred years for those mutations to become apparent. See what I mean?" "I do," said Barling. "And that's precisely why I think we ought to fight this thing together. I had an idea, you helped me with it. We can continue like that." "Well," Steve nodded, "we have a first-class problem on our hands. We can't do anything about it until we know what's going on--only the mystery's a little deeper than you think. First, I heard a voice out on Ganymede. My brother's voice." "Your brother's?" Barling scratched his head. "Oh, wait a minute! You must mean Charlie Stedman who was killed out here a few years back?"