When scientists exploring the Amazon River stumble on a “missing link” connecting humans and fish, they plan to capture it for later study. But the Creature has plans of his own, and has set his sights on the lead scientist's beautiful fiancée, Kay.
A dangerous combination of radiation and insecticide causes the unfortunate Scott Carey to shrink, slowly but surely, until he is only a few inches tall. His home becomes a wilderness where he must survive everything from spiders living in the cellar to his beloved cat.
Lin McAdam rides into town on the trail of Dutch Henry Brown, only to find himself in a shooting competition against him. McAdam wins the prize, a one-in-a-thousand Winchester rifle, but Dutch steals it and leaves town. McAdam follows, intent on settling his old quarrel, while the rifle keeps changing hands and touching a number of lives.
