What is the theme of "Hearts and Hands" by O. Henry?

In many of his stories, O. Henry holds the universal romanticized wish that people are intrinsically good and unselfish. This wish is exploited in the short story "Hearts and Hands." In fact, the title of this story suggests the theme that people will display "heart," or kindness, for others with no self-interest.

After they are seated across from the pretty young woman, the glum-faced man identifies the younger man handcuffed to him as the marshal....

In many of his stories, O. Henry holds the universal romanticized wish that people are intrinsically good and unselfish. This wish is exploited in the short story "Hearts and Hands." In fact, the title of this story suggests the theme that people will display "heart," or kindness, for others with no self-interest.

After they are seated across from the pretty young woman, the glum-faced man identifies the younger man handcuffed to him as the marshal. Miss Fairfield, who has recognized this younger one as one of her society, is relieved to know that he is no prisoner.

This glum-faced man asks Miss Fairfield to entreat the marshal to speak on his behalf when they reach Leavenworth prison. But, that it is he who possesses an unexpected kindness becomes known only in O. Henry's ironic reversal. For, two other passengers remark upon what has occurred with the interchange of the pretty young woman and the two men who are handcuffed together. The one, who has overheard the glum-faced man identify the younger man as the marshal, remarks to the other about the kindness of this man:

"That marshal's a good sort of chap. Some of these Western fellows are all right."

 "Pretty young to hold an office like that, isn't he?" asks the other man.

The first one exclaims with disbelief,

"Young!...didn't you catch on? Say--did you ever know an officer to handcuff a prisoner to his right hand?"

Ironically, it has been the glum-faced man who is the marshal. But, he has extended kindness and "heart" to his prisoner by pretending to be the convict who is going to prison.