He took quick aim at a distant tree and pressed the trigger. There was a twang as the arrow was ejected. He jerked the sliding pistol grip forward and back to reload, pressing the trigger an instant later. Another arrow went its way.

By the time he had fired the tenth arrow in the magazine he was shooting at the rate of one arrow per second. On the trunk of the distant tree, like a bristle of stiff whiskers, the ten arrows were driven deep into the wood in an area no larger than the chest of a prowler or head of a unicorn.

“This is better than I hoped for,” he said to George. “One man with one of these would equal six men with ordinary bows.”

“I’m going to add another feature,” George said. “Bundles of arrows, ten to the bundle in special holders, to carry in the quivers. To reload the magazine you’d just slap down a new bundle of arrows, in no more time than it would take to put one arrow in an ordinary bow. I figured that with practice a man should be able to get off forty arrows in not much more than twenty seconds.”

George took the bow and went back in the cave to add his new feature. Humbolt stared after him, thinking, If he can make something like that out of wood and unicorn gut, what would he be able to give us if he could have metal?

Perhaps George would never have the opportunity to show what he could do with metal. But Humbolt already felt sure that George’s genius would, if it ever became necessary, make possible the alternate plan for leaving Ragnarok.

The weeks dragged into months and at last enough snow was gone from the Craigs that Humbolt and Dan Barber could start. They met no opposition. The prowlers had long since disappeared into the north and the unicorns were very scarce. They had no occasion to test the effectiveness of the new automatic crossbows in combat; a lack of opportunity that irked Barber.

“Any other time, if we had ordinary bows,” he complained, “the unicorns would be popping up to charge us from all directions.”