In Volume 1, Chapter 3, Mrs. Fletcher asks Magawisca to interpret and clarify Nelema's somber prediction about her children. A sense of dramatic irony mounts as Magawisca nervously tells Mrs. Fletcher some but not all of what she knows:
“That which I may speak without bringing down on me the curse of my father’s race, I will speak. This,” she added, unfolding the snake’s skin, “this betokeneth the unseen and silent approach of an enemy. This, you know,” and she held up the rattle, “is the warning voice that speaketh of danger near. And this,” she concluded, taking the arrow in her trembling hand, “this is the symbol of death. [...] I have said all that I may say,” she replied.
Magawisca clearly knows more than what she is saying. Her "trembling hand" and her agitated body language in the preceding passage indicate that she is emotional about what she knows and what she is concealing. She claims that she is saying as much as she can say "without bringing down on me the curse of my father's race." Magawisca has a sense of loyalty and duty toward her father, Mononotto. But she also has a sense of loyalty and duty toward the Fletchers. As she tells Mrs. Fletcher, she feels well cared for by their family. She wants to warn them that they are in "danger" from an "enemy," but she can't give away details of her father's plan. Nelema, likewise, seems to have been distressed to think that the Fletchers were in danger. She left the snake skin, the rattle, and the arrow to signal as much without fully betraying her people.
Dramatic irony drives the suspense of the plot here. Mrs. Fletcher is in the dark about what the danger will look like, and although the omens make her nervous, she is hesitant to take them as a threat she needs to deal with immediately. The reader knows that the plot demands the omens to be meaningful, so Mrs. Fletcher's failure to take them even more seriously feeds the suspense. The desperate dance both Magawisca and Nelema must do to protect the Fletchers while remaining loyal to their people is emblematic of something Sedgwick wants to convey: women and children are caught here in a conflict among men. Mrs. Fletcher, too, is caught in a trap that is meant to send a message to her husband; even though she does not fully understand the conflict, it ends up killing her anyway.
In Volume 2, Chapter 4, dramatic irony builds as Everell misinterprets Hope's feigned cheerfulness as happiness to be spending time around Sir Philip at Governor Winthrop's house. The dramatic irony hits its peak when Everell witnesses Sir Philip's ill-fated marriage proposal to Hope:
At this moment, when Hope stood stock still from surprise, confusion, and displeasure, Everell crossed the walk. The colour mounted to his cheeks and temples, he quickened his footsteps, and almost instantly disappeared.
Hope is in fact acting cheerful to disguise her real feelings: she has realized that she has romantic feelings for Everell, but she has pledged to help Esther win his affection. She does not want Esther or Everell to suspect that she is sad not to be pursuing Everell herself. Hope's forced cheerfulness and avoidance of Everell makes both Everell and Sir Philip alike think that Hope's romantic feelings are directed toward Sir Philip.
When Sir Philip takes the opportunity to propose to Hope, Everell only sees Sir Philip kneeling and reciting verse. Hope is so surprised that she simply freezes instead of outwardly expressing right away that she is "displeased." Everell sees Hope standing "stock still" before the man proposing to her and gets upset because he is harboring his own romantic feelings for Hope, and he assumes the proposal is wanted. Seeing Everell helps Hope clarify to herself that she does not want to marry Sir Philip, but the romance plot is far from resolved because the only people who have confessed their feelings (Sir Philip and Esther) have been rejected by the people they wanted to marry.
Still, the dramatic irony of this scene moves the romance plot forward by creating conflict that the reader knows Hope, Everell, and Esther as well must overcome. Each of them is part of the way to realizing and declaring what they want, and the fact that there has been one failed marriage proposal adds a sense of urgency to the process of getting all the way there before someone ends up married to the wrong person.
In Volume 2, Chapter 6, Hope evades capture by sneaking onto a boat that turns out to be manned by an Italian Catholic named Antonio. Dramatic irony helps facilitate Hope's escape: she lets Antonio believe that she is his patron saint, Petronilla:
Before she parted from her votary, she said, “I give thee my blessings and my thanks, Antonio, and I enjoin thee, to say nought to thy wicked comrades, of my visitation to thee; they would but jeer thee and wound thy spirit by making thy lady their profane jest. Reserve the tale, Antonio, for the ears of the faithful who marvel not at miracles.”
Hope genuinely tries to correct Antonio when he first suggests that she is the Virgin Mary, and then runs through a list of other saints she might be. Finally, she decides she has tried hard enough at honesty and instead chooses to use Antonio's mistake to her advantage. She asks Antonio here not to repeat to others that he saw her, unless they are as religious as him. The reason she gives him is that others are not as faithful, will not believe him, and don't deserve to hear of the miracle. This reason is designed to make Antonio feel special for being an extremely devout Catholic: he is one of the privileged few who is allowed to see a saint in the flesh. Through flattery, Hope achieves another, hidden objective. She doesn't want anyone to know where or how she escaped, so she needs Antonio to keep quiet. If Antonio believes that his vision of "Petronilla" needs to be jealously guarded from doubters, Hope will be able to remain inconspicuous.
Hope's quick-witted nature stands out against Antonio's foolishness. This portrayal of a Catholic man is not especially flattering. Antonio is so wholly devout that he loses his senses and won't believe Hope when she tells him that she is not a holy apparition. Hope, meanwhile, displays good character by trying to correct him but ultimately thinks on her feet about how to use the situation she is in to her advantage. Dramatic irony provides a sense of comic relief, and it also lets the reader see that Hope is principled without being too rigid to adapt to the situation.
In Volume 2, Chapter 11, when Hope orchestrates Magawisca's escape from jail, dramatic irony makes the scene both comedic and suspenseful. Hope and Magawisca must work together to stay one step ahead of Barnaby as they sneak Magawisca out in Cradock's clothing:
Hope was alarmed by the sudden increase of light—“lend me the lamp, Barnaby,” she said, “to look for my glove—where can I have dropped it? It must be somewhere about here. I shall find it in a minute, Master Cradock, you had best go on while I am looking.”
Magawisca obeyed the hint, while Hope in her pretended search, so skilfully managed the light, that not a ray of it touched Magawisca’s face.
Hope has not really dropped a glove. She makes this story up so that she can take the lamp from Barnaby and position it such that Magawisca remains in shadow. Barnaby is supposed to inspect whoever is leaving the jail to make sure no one is doing exactly what Hope is doing: sneaking someone out in a disguise. Hope goes on to distract Barnaby by asking him to talk about his grandchild. Meanwhile, Magawisca remains entirely silent and goes along with Hope's improvisation. Hope explains away Magawisca's silence by suggesting that Cradock is having "one of his silent fits."
The way Hope and Magawisca manage to keep Barnaby from realizing what is going on contributes to the reader's sense that they are the cleverest characters in the novel. Hope especially conforms to the stereotype of a clever white woman who is able to use her air of innocence to manipulate people into doing what she wants. She talks Cradock into wearing his cloak in unseasonable weather, and before he knows it he is in the jail and swapping places with Magawisca. She also cries on command in front of Barnaby to convince him to let her and Cradock into Magawisca's cell in the first place.
The novel represents Hope's cleverness favorably. However, there is a darker side to the kind of femininity she is performing here. Hope's interests mostly align with Magwisca's, but she could just as easily have used her skills to convince a court to execute Magawisca if she had something to gain from that outcome. As it is, Hope wants to save Magawisca not just out of the goodness of her heart, but also because she is a link to Faith. Sedgwick is interested in empowering young white women reading her novel to, like Hope, influence politics by influencing men's emotions and opinions. It is important to recognize that historically, white women have often exerted this influence to their own benefit and at the expense of more marginalized people.