A killer is cleaning up the streets of Milan by murdering those considered as deviant. An ornamental dragonfly, soaked in the blood of the victim, is left on each body.

Sando Kid is a medic on the battlefields of the civil war and a pacifist. One day he witnesses Yankee captain Grayton ruthlessly killing wounded and unarmed soldiers. He manages to survive thanks to the help of a friend and learns how to use a gun. From now on, he will sign up to the rangers and hunt down bandits. He soon crosses paths with Grayton again, who now has become a ruthless business man, trying to rob farmers of their land. Together with his henchmen, Grayton might be more than Sando Kid can handle, if it wasn't for Dollar, a black-clad bounty hunter who likes to wear a chain of teeth around his neck, and really likes the Kid.

Sam Foster, a bounty hunter, is wounded during a shootout and took refuge at the home of Jimmy and Mary, two brothers who live in a small farm. She cared for and healed him, explaining the concern he feels for his brother to the company he keeps. Sam discovers that Jimmy is one of the outlaws pursued and, despite their friendship, goes on his quest to catch a bandit.