Thomas Jerome Newton is an extraterrestrial from the planet Anthea, which has been devastated by a series of nuclear wars, and whose inhabitants are twice as intelligent as human beings.

When he lands on Earth - in Kentucky, disguised as a human - it's with the intention of saving his own people from extinction. Newton patents some very advanced Anthean technology, which he uses to amass a fortune. He begins to build a spaceship to help the last 300 Antheans migrate to Earth.

Meanwhile, Nathan Bryce, a chemistry professor in Iowa, is intrigued by some of the new products Newton's company brings to the market, and already suspects Newton of being an alien.