This short story by Twain presents his primarily American readership with a sense of what virtues should define them as American. It also challenges them to think of what they might do in the protagonist’s situation. This work begins with the protagonist, Henry Adams (deliberately representative of any "average" American man) being washed out to sea while on a leisurely boat trip. Rescued by a passing British ship, he ends up in London with nothing; the few possessions he had were washed away by the sea. While searching for food, the stranger is spotted by two English brothers of wealthy means, who decide to make a wager on his character. The brothers hand him a million-pound bank note: one of only two ever minted. One brother, Brother A, believes he will do the foolish thing and try and cash it at a bank. This action would lead to investigation and prosecution, given the note’s rarity and the fact that Henry would have no proof of having obtained it honestly. Brother B, on the other hand, believes that Henry will make better use of the note and offers him a job with good pay as a reward for his doing this.

Henry had not been aware of how much money he had actually been given, since the note was concealed in an envelope. However, after being given credit at a restaurant and a clothing store simply for the prestige of possessing such a vast sum of money, he realizes the power it affords him and relishes his new freedom. London society responds with much excitement to the mysterious newcomer, and Henry soon finds himself invited to a dinner party hosted by the American ambassador, where he meets two more important characters.

Portia is a young woman of the British aristocracy, with whom Henry is immediately enchanted. He even tells her the reason for his great wealth, at which she inexplicably begins laughing. Henry also meets Lloyd Hastings, an old friend and associate from his days as a miner in California, who has come to London to sell off his mining shares. Though at first Henry finds it hard to turn his mind from thinking about Portia, he responds positively to Lloyd’s request for help, discussing Lloyd’s shares with as many people as he can, and thus allowing his prestige to gild the shares that Hastings is selling. Soon, Henry, with whom Lloyd had agreed to split any earnings from the shares, has a million dollars all his own, and at the end of the month, he returns with Portia to the brother’s house. There, she reveals that Brother B is in fact her stepfather and that he told her about his wager. Henry asks for Brother B’s blessing in marrying Portia, and he has his request granted. The pair lives happily ever after, with the (now cashed) bank note hanging in a frame on their wall as a memento of how they met.