Deerslayer eludes his pursuers so that Chingachgook and Hist can get into the canoe. By giving the canoe a quick and powerful shove into the lake, Deerslayer provides his friends with their chance to reach safety. His own escape is endangered by a Mingo who seizes him, and Deerslayer loses any advantage in the fight by devoting his attention to his friend's plight. More savages reach the shore, and the uneven struggle results in Deerslayer's capture.
The Indians are elated by the sight of such an important enemy as their prisoner. Rivenoak, the chief, is especially pleased by Deerslayer's capture. Deerslayer's honor, valor, and shrewd tactics have won the respect of the Mingos; and Rivenoak proposes that Natty join the Indians by returning to the ark and then betraying his comrades for part of the expected booty. Although Deerslayer admits that Tom Hutter and Hurry Harry are no true friends of his because of their unscrupulous actions, he refuses to play the part of a traitor. Rivenoak is also impressed by Deerslayer's explanation that he came into the Mingo camp on a mission of rescue for a friend and not to take scalps. However, Catamount, who hoped to have Hist as his squaw, tries to antagonize Deerslayer; but the latter fends off the Indian's insults.
Everyone, including Deerslayer, is surprised by the appearance of Hetty Hutter, but the Indians, because of their previous respect for a person favored by the gods, do not take her prisoner. Hetty explains to Deerslayer, who also enjoys some freedom of movement because of the Indians' admiration. of his prowess, that Judith has sent her on this errand. Judith will meet Hetty offshore in a canoe. Hetty is to try to ransom Deerslayer as Tom Hutter and Hurry Harry were previously ransomed. Deerslayer, however, warns Hetty that the Mingos are undoubtedly plotting to seize the two girls — and the canoe so valuable for a raid on the ark.
The Mingos, believing that their sentry will watch Hetty, allow her to wander away from the camp, so Hetty is able to make her escape to rejoin Judith in the canoe. The Mingo sentry was waiting for an Indian maiden to join him in an apparently prearranged tryst and failed to observe the white girl carefully. When the two sisters meet again in the canoe, Hetty is very blunt about Deerslayer's chances for rescue, and Judith betrays the increasingly tragic aspect of her love for Deerslayer by promising to do anything to save him.
A shot sounds in the silence of the night, and the Mingo girl who was to meet the sentry is mortally wounded. Judith realizes that the shot must have come from another canoe or from the ark. She also understands from a swift glance at the Indian camp that the Mingos are infuriated at this unjustified atrocity and that Deerslayer is now in more mortal danger than previously. The girls paddle quickly to safety in the center of Glimmerglass.
Deerslayer's successful effort to save his friends at his own expense is interpreted by Cooper as the generosity that would have made a Roman famous for all time. Deerslayer, then, is as noble as the characters in classical antiquity, and America can produce epic heroes in the tradition of European models. Deerslayer is likewise "the innate gentleman," as Cooper defines his American hero, and this proud, honorable behavior by Natty Bumppo merits a correspondingly chivalric treatment from his savage captors. The two white men, Tom Hutter and Hurry Harry, are mutually scorned and despised by Deerslayer and the Indians because they adhere to no code of honor. The confrontation between Deerslayer and the Mingos is characterized by lofty ideals and elevated speech; they resemble medieval knights who face each other knowing they owe allegiance to the bond of knighthood.
In the scene with the Mingos, Deerslayer again uses his term, "sarcumventions," to distinguish between the conduct of an honorable white man and an honorable Indian. A Mingo, as Deerslayer explained previously, can use — and should employ — circumventions to achieve his purpose. Deerslayer, however, must reject such tactics. For example, Deerslayer's rejection of Rivenoak's offer of an alliance and membership in the tribe (in exchange for betrayal of the ark) wins the white man added respect from the chief. Such a maneuver is a justifiable and honorable part of a Mingo's code, but a white man cannot resort to such "sarcumventions." In short, Deerslayer's code is put to a crucial test because his life hangs in the balance. His code, based on the gospel, does not permit a Christian white man to do what is acceptable among the Indians.
Two clues to future action — a regular feature of Cooper's literary technique — are provided: Deerslayer's explanation to Hetty of his sentence of torture and death at the stake gives an expectation of suspense and excitement to coming chapters, and Deerslayer's telling Hetty that troops from the nearest garrison may soon hear of the Mingo war party and arrive at Glimmerglass in a day's march indicates the author's solution to his hero's predicament.
In Chapter 18, Cooper utilizes three devices common among the romantics: escape and pursuit, the meeting and pairing of opposites, and the Gothic atmosphere of terror, night, and mystery. The first and third devices stress physical action and movement while the second is a lull in motion because of the dialogue between the two sisters. The violent return to the main plot problem — Deerslayer's captivity — brings the hero's fortunes (and those of the innocent girls) to a more dangerous low point. There is the renewed portrayal of contrasts between Judith and Hetty when the two sisters are reunited in the canoe. This scene is also one of the few occasions when the girls talk alone in The Deerslayer. Romantic irony is very evident in the meeting: Judith, more intelligent and experienced, appeals to Hetty for her advice and judgment; and Hetty's answers are innocently — and correctly — stated. Cooper is the moralist in depicting Judith's change and reform. Judith knows that Hetty's list of Deerslayer's defects (he is very plain and cannot read) would have eliminated him as her suitor in the past when she was attracted to the officers in the nearby fort. Judith now accepts her position as one of inferiority to Deerslayer's moral stance, and she even wonders about the possibility of attaining that higher level. Deerslayer, as Cooper remarks, is obtuse in matters of love and is still unaware of Judith's growing devotion. Judith's hopes and desire for improvement are ironically, and later tragically, doomed by Deerslayer's failure to recognize her love. In her honest, ingenuous way Hetty is the voice of morality (and Cooper) to indicate to Judith the stern commands of a simple, pure life which the latter has not followed.