Life is rough in the coal mines of 1876 Pennsylvania. A secret group of Irish emigrant miners, known as the Molly Maguires, fights against the cruelty of the mining company with sabotage and murder. A detective, also an Irish emigrant, is hired to infiltrate the group and report on its members. But on which side do his sympathies lie?

A newspaper publisher, wanting to prove a point about the insufficiency of circumstantial evidence, talks his possible son-in-law Tom into a hoax in an attempt to expose ineptitude of the city’s hard-line district attorney. The plan is to have Tom plant clues leading to his arrest for killing a female nightclub dancer. Once Tom is found guilty, he is to reveal the setup and humiliate the DA.