The plot involves Aldo Ray unexpectedly finding himself with mob money. Rudy Bond takes pleasure in killing people, structuring his actions as if it were some kind of competition for them. Brian Keith collaborates with Rudy Bond, but finds him repulsive, until the sadist attempts to kill him. James Gregory is looking into these events and feels overwhelmed by the situation; he shares his worries with his spouse. Does this sound familiar? It’s because this was the original version that McCarthy later adapted into a more conventional Hollywood style, but this one remains authentic. The villains here are just as vulnerable as the heroes. They aren't portrayed as invincible figures, which is likely too much for audiences accustomed to simplistic entertainment. This is a sophisticated presentation—a genuine portrayal of fully realized characters; or, as it’s been described, “believable people in extraordinary situations,” and that's what distinguishes timeless films from failures. A significant portion of the story unfolds through flashbacks, which I typically dislike, but this film remains a classic because the characters are so believable.

Source on TMDB