Earth Alert!

Calvin practiced teleportation for endless hours. He kept the metal ball Forential had given him in almost constant motion. He would exclaim delightedly and hurl it toward one of the twenty-seven other mutants in his compartment. Until the time he hit John in the back of the head with it, his intended victims had always parried it. John lay in a pool of blood, and Calvin began to cry--loud, shrill wails of despair and contrition. When Forential came, he knew instinctively what had happened. Calvin represented the only failure the aliens had experienced in their mutation program; ten years ago his mind had ceased to develop.