An unnamed operative of the Continental Detective Agency arrives in rural Personville at the behest of a local newspaper publisher, whose murder prompts the Op to spark a war between the gangs that have taken over the town. Donald Willsson's death left the Op in the hands of his son, Elihu Willsson. Elihu offers him $10,000 to clean up the town of all its gangsters.
The Op weasels his way into the good graces of each of the gang leaders individually, by pretending to be crooked or offering to spy on the others. He also ingratiates himself to Noonan, the town's corrupt police chief, and Dinah Brand, girlfriend to one of the gangsters.
Using information from Dinah and Noonan, the Op leaks information to his gang contacts about a recent heist, which was staged to blame one of the competing gangs. Soon the gangsters are all gunning for each other, which the Op hopes will leave them all dead.
However, someone kills Dinah and frames the Op for it. He visits Reno Starkey, a surviving gangster, and encourages him to go after Pete the Finn (the other big gangster still standing). The two kill each other, along with Noonan, and Starkey confesses that he killed Dinah and set up the Op to take the fall.
With all the gang leaders dead, the Op convinces Willsson to call the governor, who declares martial law in the town and sends the National Guard to take over for the corrupt police department. The Op returns to San Francisco, where his agency is based.
Best part of story, including ending:
This isn't the first time someone on the side of justice has played multiple groups of criminals against each other, but it might be the smartest and dirtiest. The Continental Op is willing to do anything to get the gangsters to kill each other, and it works.
Best scene in story:
When the Op arrives in town, he meets with Donald Willsson's wife, who tells him that her husband can't see him that night. The Op leaves, noting a spot of blood on her shoe -- one small detail in her otherwise clean and well-kept home. That blood is like the first drop of water that spills out of a dam before it breaks and unleashes a torrent of violence.
Opinion about the main character:
The Op plays his cards close to his vest, such that you don't know what he's going to do next. He's also just sleazy enough that you start to wonder, every time he goes to talk to a gangster, whether he's working an angle that will enrich or otherwise benefit himself rather than achieve the justice he was hired for.