Out of the star gulfs he came, troubled, searching, with a warning for Earth no one dared ignore. Never would Earth see his like again-or know the reason why! The alien's mission was grim, purposeful, and scientific. It was only natural that he should mistake men for machines and machines for men. Earth's terrible predicament was not of his making, but it came close to destroying Man. The book comprises two short novels, one written by Hal Clement, the other by Sam Merwin Jr. Clement's portion is written from the alien's point-of-view. Merwin's is from man's point-of-view. Combined, they form a unique narrative. It can be read three ways: Clement's alien novel skipping from first, to third and so on-Merwin's human story, taking on the even chapters. Or, just read the story from front to end! First published in Satellite Science Fiction for February 1957.