Fifty spaceships, each three miles across, hover ominously above Earth's major cities. The Visitors that emerge are humanlike in appearance and extend the hand of friendship. Our planet's resources are just what these aliens need to survive. And for its future survival, unsuspecting humankind will need... a miracle!

Zack Mayo is an aloof, taciturn man who aspires to be a navy pilot. Once he arrives at training camp for his 13-week officer's course, Mayo runs afoul of abrasive, no-nonsense drill Sergeant Emil Foley. Mayo is an excellent cadet, but a little cold around the heart, so Foley rides him mercilessly, sensing that the young man would be prime officer material if he weren't so self-involved. Zack's affair with a working girl is likewise compromised by his unwillingness to give of himself.

In the late 19th Century, Mary Breydon, a widow, and Peggy Breydon, her daughter manage a stagecoach stop on The Cherokee Trail. The story is told from the perspective of Peggy, looking back on her adventures.