Summoned from Earth by magic, Dave Hanson finds himself embroiled in the politics and engineering problems of an alternate Earth named Terah...for Terah's sky has shattered, and he may be the one man in all the universe who can restore it! But science and sorcery, beautiful women, and fantastic monsters are just the beginning of his problems...

Originally published in shorter form in Beyond Fantasy Fiction in 1954, then expanded to novel length, here is Lester del Rey's classic science-fantasy, The Sky is Falling!