They did not know. They only knew that the enraged creatures were closing in on them, closer and closer--and now the ships were being sent back to the system as rapidly as possible--one--two--three--four--but more could not get through--the others were cornered, marooned in infinity by the destruction of the sender. The Force Creatures, utterly immune to the Minus Force shells, attacked unchecked, gripped it with strange forces, limbs, hands or gripping force, that tore through the foot-thick alloy like so much tissue paper, metal, which was fifty times as strong as our frail steel, a metal whose molecules had been designed by the scientists of the race millions of years ago, and in all those ages no stronger, more inert metal had ever been found. But now that tough envelope was torn open, for the forces of atoms were greater than the forces of molecules, and the creatures used those forces. But those marooned ships were lost--destroyed soon by the vengeful giants. And the forces of man on the far-off planets of a far-off sun were worried anew. Their weapon was a failure after all. Some new thing must be developed. But how did it happen that the first attempts were successful? The scientists believed it was due to the fact that the first attempts were utter surprises to the creatures--they were taken before they could prevent the loss of their energy. In some way they were able to build a barrier about themselves that prevented the loss of energy, even as it prevented the penetration of the energy of the disintegration ray. But man must develop some new, some stronger weapon. The time was getting too short for more failures. For Hal Jus had announced a discovery that made men even more anxious to abandon their age-old home. The Sun was to become a nova. These flaming stars had been known and studied for ages. Dim, old stars they were that suddenly flared up for a brief period of intense activity, then quickly faded back even lower than before. It behooved man to move quickly. A mighty people that for ten billion years had slowly built up the mighty structure of their science had to move. Many weapons were tried, many expeditions of two or three ships made the trip, and attempted to destroy the creatures. Some succeeded moderately well, others met with ghastly failure.