Huck comes upon Mary Jane, who is packing for her trip to England. She is also crying because, in selling the Wilks’s slaves, the duke and king separated a mother from her children. Moved by her tears, Huck blurts out that the family will be reunited in two weeks, and, thinking that in this case the truth is better than a lie, he says he can prove it.
It is maybe because Huck recognizes just how big Mary Jane’s heart is here—she is crying out of an empathy with the slaves—that he decides to trust her with the truth, as he trusts only Jim. Huck’s trust in Mary Jane makes telling the truth practical.
Huck reveals that the duke and king are not Mary Jane’s uncles but rather a couple of frauds. Mary Jane indignantly wants to have the duke and king tarred and feathered. Huck says he would tell on the duke and king immediately except that he would be endangering someone (Jim), and he proposes a different plan.
Huck has grown up enough at this point that he discourages Mary Jane from immediate action, which would be efficient and practical, in favor of a course of action that is maybe less efficient but more sensitive to Jim’s condition and needs.
Huck tells Mary Jane to go away, because he is afraid that she will express in her face knowledge of the duke and king’s fraud, which will in turn allow the two to escape. Mary Jane is to return in the evening, after Huck and Jim have made their escape, and expose the duke and king, sending for the townspeople of Bricksville, the site of the performance of The Royal Nonesuch, as witnesses regarding the duke and the king's trickery. Huck also gives Mary Jane a note explaining where he has hidden her bag of gold. Mary Jane promises to remember Huck forever and pray for him, and, though Huck says he has not seen Mary Jane since, he thinks of her often.
Mary Jane has a strong sense of justice, one that in its earnestness and self-consistency strongly contrasts with that of society at large, but it is precisely the strength of her feeling that makes her a liability in exposing the duke and king. Unlike Huck, she does not have the freedom of character that would enable her to dissemble, or act, as Huck does, and so she would give the duke and king a chance to escape.
After Mary Jane lights out, Huck runs into her sisters. Huck lies that Mary Jane has gone to visit a sick person in town, and, though the girls press Huck on the facts of his story, he at last tricks the two into not mentioning anything to the duke and king that might alert them to Mary Jane’s knowledge of their fraudulence.
Huck may decline to tell Mary Jane’s sisters the truth because he doesn’t trust them sufficiently, or maybe because it is more practical for only one sister to know the truth, so that there are fewer people who could tip the duke and king off, even accidentally, that their cover has been blown.
Later that day, the duke and king hold an auction to sell off the Wilks estate. As the auction draws to a close, a steamboat lands, and a noisy crowd approaches, singing out that in their company are none other than two men who claim to be Harvey and William Wilks.
The duke and king are astonishingly able to get away with auctioning off the Wilks estate despite the suspicion Dr. Robinson cast on them. The townspeople are so taken by the con men that they only test their assumptions when directly contradicted.