On the ark Hurry Harry and Tom Hutter have been awakened by the returning Chingachgook and the rescued Hist with the news that Deerslayer is a prisoner of the Mingos. Neither one of the two white men greatly regrets Deerslayer's misfortune: Hurry Harry is jealous of Judith's attentions to his rival, and Tom Hutter resents the young man's honesty and idealism. It is now that we learn the circumstances of the rifle shot and the cry of agony. It was Hurry Harry who impetuously fired the shot in the dark because he had heard the exclamation of the Mingo sentry seeing the ark close to shore; it was his bullet which caused the accidental death of the Indian maiden. Hurry Harry, initially disturbed by Hist's furious criticisms, is as little disturbed finally by her promised wrath of Manitou, the Indian deity, as he is of possible punishment by the Christian God. Tom Hutter, nevertheless, criticizes his companion in crime for making their situation worse.
There is an increasing mood of dislike and distrust between the two Indians and the two white men, but they are necessary allies in a perilous position and must co-operate. Determined to make a strong stand at Muskrat Castle, Tom Hutter guides the ark in that direction as Judith and Hetty approach them in the canoe. A spyglass gives the white men an advantage in concluding that the castle has not been occupied by the Mingos. However, Chingachgook and Hist see a moccasin floating near one of the foundations of Muskrat Castle, and Chingachgook goes alone in a canoe to recover the moccasin before the ark docks at the castle. The white men are still skeptical about any Mingo threat: The identification of the moccasin as Mingo only emboldens Tom and Hurry Harry to land. The white men ignore Chingachgook and Hist's conclusion that an ambush awaits them, and they even leave their guns on the ark upon entering the castle. At first, no indication of Mingo intruders is evident; but the two white men are suddenly and ferociously attacked by Indians as they penetrate the castle. Hutter is quickly tied up by the Mingos, but Hurry Harry battles desperately to save himself. Rivenoak had disarmed his warriors because he wanted the white men taken alive, and the fight is consequently one of brute strength.
Hurry Harry is finally subdued by the Mingos, and they tie him up beyond any apparent hope of escape. Chingachgook and Hist, dismayed by their inability to help the two captives, try to maneuver the ark to the open lake in order to elude capture and to warn the two sisters who are approaching in a canoe. However, the wind and the current are against the ark so that the ship is slowly drawing closer to the castle. On the platform of Muskrat Castle, Hurry Harry sees a chance for escape. He shouts to Chingachgook and Hist on the ark, and they prepare to save him as he rolls toward the ship. Hurry, however, lands in the water and is dragged along with a rope in his teeth and hands as the ark now escapes from Muskrat Castle.
Hurry is dragged aboard the ark as it skims the surface of Glimmerglass. Three Mingos pursue the ark in a bark canoe, but they soon realize the impossibility of overtaking the ship and the unfavorable odds in case of a fight with its defenders. The Indians see a better target for their attack: the canoe with Judith and Hetty. A chase takes place across Glimmerglass. Each side has advantages: the girls are lighter in weight, but the Mingos have two paddles and three paddlers so that a fresh pair of hands is always in motion. The Mingos are also stronger than their feminine opponents, and they gradually reduce the distance between the canoes. Then one of their paddles breaks, forcing them to abandon the chase. Returning to Muskrat Castle, the Mingos leave after a time and the hungry girls go there. Judith sends Hetty into the castle first because she knows that the Mingos will not harm Hetty because of her mental condition. Hetty's strange report that their father is apparently sleeping leads to Judith's investigation of the premises and her discovery that Tom Hutter has been stabbed and scalped and is dying.
Cooper is at his best in these two chapters of dynamic and exciting episodes as the Mingos and their enemies come to open warfare on land and on Glimmerglass. There are no long, digressive moments of describing either the beauty of the lake, the surrounding woods, the sunset, or the sunrise. All the previous descriptions have provided abundant details of the physical setting, and the novelist can proceed at a rapid pace in telling his story. Significantly, perhaps, Deerslayer vanishes completely (his name is seldom mentioned) from the action, and his fate seems settled. Deerslayer's absence likewise appears to be a sign that the fortunes of the besieged group are declining: Judith and Hetty are in danger as they attempt to reach the relative security of the ark; Hurry Harry is exhausted after his harrowing experience at Muskrat Castle; and Tom Hutter is close to death. Only the two Indian allies, Chingachgook and Hist, have, ironically, eluded any serious encounter with the Mingos.
The fault for the disastrous turn of events is correctly placed upon Hurry Harry. He is clearly the villain of the novel because his heartless (though technically innocent) murder of the Mingo girl has accentuated the downward trend of fortune for Deerslayer and the others. Hurry Harry's bragging and bravado also unfortunately influence the more cautious Tom Hutter. The primary cause of Hurry Harry's villainy or evil nature is the omission of a "moral sense," in Cooper's repeated phraseology. For example, Hurry Harry at the beginning of Chapter 19 callously blames Deerslayer for allowing himself to prowl about the Mingo camp and be captured. Ironically, Hurry Harry did exactly the same thing, and was rescued from captivity by Deerslayer, whom he now renounces. Hurry Harry is impetuous in his disregard of the signs and warnings about a Mingo ambush in Muskrat Castle, and he is thus responsible for Tom Hutter's scalping and death. Hutter, of course, has been guilty of crimes and has been a willing accomplice of Hurry Harry, but in these chapters Hurry Harry has revealed himself to be the moving force behind the actions leading to disaster and tragedy.
Cooper refers to Hurry Harry as "the handsome barbarian," and the romantic device of the ugly versus the beautiful is observed in the contrast between the plain but honest Deerslayer and the handsome but wicked Hurry Harry. By eliminating Natty Bumppo and placing all the decisions (and mistakes, thereby) in Hurry Harry's hands, Cooper has inverted his usual procedure of bringing his epic hero to the forefront of the story. The villain dominates and destroys the efforts of the outnumbered defenders.
Although the ambush at Muskrat Castle effectively uses the elements of suspense, mystery, and excitement, the escape of Hurry Harry has been rightly criticized for its violation of verisimilitude. Cooper, though he thrills his readers, has not rendered this episode plausible: It is difficult to accept Hurry Harry's agility to tumble from the castle platform, hold a rope between his teeth and tied hands, and be dragged to safety aboard the ark. On the other hand, the chase of the girls' canoe by the Mingo canoe is very acceptable, and the fortunate breaking of the Mingo paddle, though very convenient, is at least believable.