Pennsylvania 1876, and there is trouble afoot in this mining town populated by Irish immigrants who are dreadfully exploited by their bosses for they have no union or other representation to prevent this. There is one thing they can do to fight back, however, or at least some of them are: as a subset of the Hibernian secret society they have created in the United States, there are The Molly Maguires, what would be classed as a terrorist organisation who make life difficult for the awful management by setting off explosives in and around the mine to sabotage it. If the bosses are listening and improve conditions, so be it - but they don't, they call in a Pinkerton detective instead.
Said detective played by Richard Harris in the role he believed scuppered his promising career as a Hollywood leading man, not that he never headlined a movie ever again, it's just that his cachet had evaporated, and it took Westerns like A Man Called Horse to give him the name above the title he thought he deserved. The Molly Maguires was an infamous flop at the time, 1970 being a year of such cinematic disasters where it was looking like the big studios were utterly out of touch with what audiences wanted to see, a fall-out from the counterculture influence on pop culture the suits in the offices were not exactly au fait with and floundered in their attempts at appealing to.
Harris's co-star Sean Connery saw his career suffer too, a mixture of the public resenting his attitude to his most famous role as James Bond which he did not appear to be overfond of in the debacle over Diamonds are Forever, and his wish to explore challenging parts in films that were not obvious box office hits now he was financially comfortable and could afford to. This state of affairs recovered by and by, and when the nineties rolled around he was as big a star as he ever was, but when you see him here in a role where he did not have any dialogue whatsoever until almost three quarters of an hour into the story, you can well see why those audiences were deciding not to bother.
Therefore the film sank without trace, an unpopular subject starring actors who were falling out of favour... but then something interesting happened to its standing. After a few television showings and eventually, release on home entertainment, it gathered a small but growing audience for whom these stars had since regained their stature and were keen to seek out their lesser known works once the more obvious titles had been exhausted, and the consensus began to alter. Now The Molly Maguires was not box office poison, but a valid examination of the immigrant experience with special attention given to how they can be taken advantage of to the point of extreme poverty, health issues and even death. These were problems that had never gone away in the years since and struck a nerve with its new cultists, who didn't mind the production's grit and lack of humour or Martin Ritt's slightly staid direction.
The Irish depicted here are initially grim-faced, insular and work as hard as they drink and play hard, with violence part of their every day life, as if the exertions and frustrations of their occupation that takes so much from them has to have an outlet somewhere, and that is to knock seven shades of shit out of each other - or any outsider who happens to cross their paths. This is strongly implied to be the driving force behind the terrorists' acts as much as it is their sense of social injustice, and once Harris's spy infiltrates Connery's cabal by winning his confidence (though interestingly, Connery's character is never wholly convinced Harris is who he says he is, but reasons if he is not he will be able to recruit him to their cause) the stage is set for betrayal, but also more mayhem in anticipation of Sergio Leone's Duck, You Sucker There was romance for Harris with Samantha Eggar whose house he boards in, but this was disposable as the really substantial relationship was between the two leading men. Incidentally, if you think this was Hollywood telling you the Irish are inherently violent, the rugby match halfway through demonstrates the Welsh were too. Music by Henry Mancini.