The narrator is sent by a friend to interview an old man, Simon Wheeler, who might know the location of an old acquaintance named Leonidas W. Smiley. The narrator finds Simon at the "decayed mining camp of Angel's". The narrator asks the fat, bald-headed man about Leonidas. Simon responds that he doesn't know a Leonidas Smiley, but he knows a Jim Smiley. Simon then tells a story about Jim.
Jim Smiley loves to bet. He bets on anything, from the death of Parson Walker's wife to fights between his bulldog pup (named Andrew Jackson) and other dogs.
Once, Jim caught a frog and named it Dan'l Webster. For three months, he trained the frog to jump. At the end of those three months, the frog could jump over more ground than any other. Jim carried the frog around in a box.
One day, a stranger to the town asks Jim what is in his box. Jim says that it is a frog that can outjump any other frog in Calaveras County. The stranger looks at the frog and responds that the frog doesn't look any different from the other frogs of Calaveras County, so he mustn't be the best. The stranger tells Jim if he had a frog, he'd bet $40 that his frog could beat Jim's.
Jim agrees to the bet and gives the box to the stranger to hold, while Jim hunts for another frog for the stranger. While Jim is catching the stranger's frog, the stranger pours lead shot into the mouth of Jim's frog.
When Jim returns, he and the stranger arrange the frogs for the contest. They align the frogs evenly, and on the count of three they let them loose. The freshly-caught frog jumps away, but Dan'l Webster doesn't budge.
Jim is surprised and disgusted. He gives the money to the stranger, and the stranger happily leaves. Jim wonders why Dan'l looks so heavy. He takes the frog and tips him upside down. The frog coughs up handfuls of shot. Jim sets the frog down and chases after the stranger. The stranger is long gone, however, and Jim never catches him.
At this point in his story, Simon is called away by someone on the front porch, and he tells the narrator to remain seated. The narrator realizes Jim Smiley isn't the least bit related to Leonidas W. Smiley and prepares to leave. Simon catches the narrator at the door and starts telling him another story about Jim's one-eyed cow. The narrator excuses himself and leaves.