The narrator is sent by a friend on an errand to visit an old man, Simon Wheeler, to find an old acquaintance of his friend, 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 of a Jim Smiley. From there Simon tells the story of 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 the box of his. Jim tells that in the box 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 than the other frogs of Calaveras county, so he mustn't be the best. He tells Jim if he had a frog, he'd bet him $40 that the frog he had could beat Jim's.
Jim agrees to bet, and he gives the box to the stranger to hold while Jim was to catch another frog for the stranger. While Jim is catching the stranger's frog, the stranger pours lead shot into the frog's mouth.
Jim was surprised and disgusted. He gave the money to the stranger and the stranger giddily left. Jim wonders why Dan'l looks all of the sudden so plumpy. He takes the frog and tips him upside down. The frog coughed out handfuls of shot. Jim set the frog down, and chased after the stranger. But the stranger was long gone, and Jim never caught up to him.
At this point in the story, Wheeler is called away by someone on the front porch, and tells the narrator to keep seated. The narrator realizes that Jim Smiley isn't the least bit related to Leonidas W. Smiley, and starts walking away. Simon catches the narrator at the door just before he leaves, and starts telling him another story, about Jim's one-eyed cow. The narrator excuses himself and leaves.