Frederik Pohl

“ I was too close to the atom-rocket. My conductor screen grazed the warhead itself!
Its energies surged through the unstable elements in the warhead; a warning bell sprang into clamorous life. The group around me froze in their tracks, mouths open, faces mirroring fright and disbelief—and the frightful power of the strained atoms within the warhead began to grind toward nuclear fission! ”

“ The ortho-history books were clear on one fact: Venus had been destroyed in the War of Annihilation by means of a hydrogen-chain reaction, the most deadly atom blast known. Atoms of hydrogen, under the influence of gamma-particle bombardment, coalesced to form atoms of helium—and all the incalculable power represented by the odd fraction of mass left over was released in the form of free energy.
But the atom-rocket before me seemed to be nothing more than a simple nuclear-fission affair! Where were the photon-exciters? ”

“ You must not interfere!
Yet I had interfered already; I had started a new time-sequence by destroying Earth's chance to wipe out Venus. If I could neutralize that act by helping them now, perhaps there would be a chance.
"I will show you how to use the katonator," I said weakly.
Silently I adjusted it, slipped the belt off and handed it to him. He led me outside to where stars blazed in a black night. He looked upward hesitantly, pointed to a brilliant blue planet.
"Is that it?" he asked one of his companions. The man nodded. Carefully he took aim, pressed the trigger as I had showed him. ”

“ Quickly I dropped the shield of my conductor screen. Trusting that my luck would hold, and the men around me would be too dazed to fire their weapons again, I drew my katonator, set it at drain, focused it on the atomic warhead. ”

“ The branches of Fan-Shaped time could never be retraced. The man who interfered with the space-time matrix, displacing even a comma in the great scroll of time, would be cut off from his origin forever. ”