The story involves the murder of one Col. Norman Bohun, a drunkard and a womanizer. The method of the murder was obvious enough: a small hammer bashed his skull in. But the manner of the murder was inexplicable, for how could such a small hammer so completely obliterate the colonel's skull as well as the helmet that he was wearing? Obviously, only someone with supernatural strength could have done it, and in retribution for all of Col. Bohun's sins. Thus, the title "The Hammer of God."
In our world of CSIs, such a plot would be cliche. In fact, such plots were already well-worn at the time the story came out, having been popularized not too long ago by the likes of Sir Arthur Conan Doyle. But with some suspenseful buildup, witty dialogue, and an eye for descriptive detail, G.K. Chesterton still manages to deliver a detective story that leaves you saying out loud: "Now, why didn't I think of that?"
Yet for all that "Hammer of God" would still be a conventional mystery if it weren't for its very unconventional detective, the unassuming yet very astute Father Brown. Like Sherlock Holmes, Father Brown is several steps ahead of the other characters and the reader. But unlike Sherlock Holmes, Father Brown is a Roman Catholic priest. His province is not crime but the human soul. As such, Father Brown is less interested in the method and more in the motive; he is less interested in bringing the criminal to justice and more in bringing the sinner to repentance. Ultimately, the key lies in his understanding of human nature.
Take the following exchange from "Hammer of God", for instance, when Father Brown confronts the criminal with his deed. Horrified at his discovery, the perpetrator attempts to commit suicide.
[He] threw one leg over the parapet, and Father Brown had him in a minute by the collar.
"Not by that door," he said quite gently; "that door leads to hell."
"How do you know all this?" he cried. "Are you a devil?"
"I am a man," answered Father Brown gravely; "and therefore have all devils in my heart...."
The last line sent shivers down my spine when I first read it. In just one line Chesterton had summarized so succinctly the source of human evil, that is, the human heart. That we are neither angels nor supermen. That we are driven by passion and desires. That even the best among us traverse life dancing a delicate dance between good and evil.