Mackenzie blasted off into the void carrying sealed orders. Once in orbit, Mac opened the orders and read a microfilm that was probably his own death warrant. In his experimental X12 vessel, Mac was ordered to an enigmatic planet on the galactic rim, a world from which no astronaut had ever returned, a world protected by a screen of barrier-rays which defied all attempts at analysis. ~ ~ Mac succeeds, but human civilization would soo wish that he had failed . . .