Natty Bumppo and Hurry Harry, about the year 1740, journey toward Otsego Lake in upstate New York. Although they are not always in agreement, the two men realize the need of each other's protection in case of attack from the Indians (Mingos). Natty, or Deerslayer, is on his "first warpath," as the novel is subtitled, because he has not yet been in combat with another man nor been forced to kill a human being; in this novel, he will be forced to kill. The two travelers, finding Muskrat Castle deserted, seek Tom Hotter and his two daughters, Judith and Hetty, in the trapper's other home, the ark. Hurry Harry, hoping to marry Judith, is treated coldly by her when the two men locate the ark, but Deerslayer is greeted warmly. Hetty is equally friendly to Deerslayer and to Hurry Harry. Suspicious at first of Deerslayer, Tom Hutter, or Floating Tom, realizes that the newcomer will be a valuable ally in case of Indian attack. As the ark is maneuvered away from shore to the open lake, some Mingos try to board the vessel; but Deerslayer proves his worth by repulsing the invasion.
The three men decide to reclaim the canoes hidden by Tom Hutter along the shores of Glimmerglass. Having succeeded in this mission for their protection and defense, Tom Hutter and Hurry Harry scheme to land in the dark, attack the sleeping Mingo women and children, and get scalps for the bounties. Although Deerslayer refuses to join this expedition, he waits offshore in a canoe for the return of Hurry Harry and Floating Tom. The Mingos are not so easily deceived, and the two white men are captured. Unable to help the prisoners, Deerslayer determines to secure the canoes first and to return to the ark where the girls are waiting.
One canoe drifts to the shore, and Deerslayer, trying to recover the boat, is met by a Mingo who also claims the canoe. Thinking that he has persuaded the Indian of the true ownership of the boat, Deerslayer turns away. In time, Deerslayer sees the Mingo preparing to shoot, and he fatally wounds the attacking Indian. Deerslayer, having experienced his "first warpath," treats his dying opponent honorably by not taking his scalp and by arranging him comfortably. The Mingos, recognizing in Natty Bumppo a great warrior, call him by a new nickname — Hawkeye.
At the ark, Deerslayer prepares to meet his friend Chingachgook, a chief of the Delaware nation. The rendezvous is perilous because the Mingos are pursuing Chingachgook. He jumps aboard the ark and barely escapes. While the friends rejoice in their reunion, Hetty surprises everyone by her decision to leave alone in a canoe, go to the Indians and try to convince the savages to release the two prisoners. Although Deerslayer tries to block her path with another canoe, Hetty eludes him and refuses to listen to his warnings.
Hetty, stumbling through the woods, meets Hist, who has been abducted by a renegade Delaware and brought to the Mingo camp. Hist is in love with Chingachgook and explains to Hetty that the Delaware chief and Deerslayer have met at Glimmerglass to rescue her. Although the Mingos refuse to listen to Hetty's pleas to release Tom Hutter and Hurry Harry, they do not harm the girl because they respect as blessed by divine protection a person of limited intelligence and simple-mindedness, such as Hetty.
Deerslayer and Judith open Tom Hutter's chest to find any items they can use as ransom for the two white men. The three exiles on the ark, intent on their investigation of the chest, are startled by the appearance of a Mingo who serves as a guide for the returning Hetty. Deerslayer shows some ivory chess pieces to the Indian who eagerly goes back to the Mingo camp with this news of a possible exchange of the pawns for the prisoners. After hard bargaining, Rivenoak, the Mingo chief who has approached the ark, accepts the ivory rooks, and Tom Hutter and Hurry Harry are set free. Learning nothing from their close call with death, the two men plot another raid for scalps on the Indian camp. They discover, however, that the Indians have moved camp, spoiling their plans.
Setting out to rescue Hist, Deerslayer and Chingachgook are dismayed to find that the new Mingo camp is at the place where the Indian girl told Hetty she would be waiting. Despite the increased danger, Deerslayer and Chingachgook plot to save Hist. In the ensuing action, Deerslayer is able to shove the canoe with Chingachgook and Hist beyond range of the Mingos, but he is pursued by the Indians and captured. Hetty is sent by Judith to the Mingos, but they refuse to bargain for such an important prisoner. Judith and Hetty, after the latter's return from her unsuccessful mission to ransom Deerslayer, travel in their canoe around Glimmerglass in search of the ark. A shot fired by Hurry Harry from the ark accidentally kills an Indian maiden who was meeting her lover on the shore.
On the ark, the four refugees (Tom Hutter, Hurry Harry, Chingachgook, and Hist) go to Muskrat Castle where the white men, ignoring the warnings of their two Indian companions about a possible ambush, enter fearlessly. The Mingos, hiding in the castle, attack, subdue, and tie up Tom Hutter and Hurry Harry. Chingachgook and Hist, helpless onlookers on the ark, maneuver the boat out of range; and Hurry Harry quickly rolls off the castle's platform into the lake where he is pulled to safety. The Mingos at first pursue the ark in a canoe, but they see a better target: Judith and Hetty in another canoe. After a chase which the Mingos almost win, one of the Indians breaks a paddle and they give up the pursuit.
When the two girls go to Muskrat Castle, they find that Tom Hutter, scalped by the Mingos, is close to death. After confessing that he is not Judith and Hetty's father, Tom Hutter dies and is buried in Glimmerglass, close to the watery grave of his wife, the girls' mother. Deerslayer, released temporarily by the Mingos, appears and announces the terms of surrender from the Indians: Chingachgook is to leave in safety, the three girls are to live with the tribe. The offers are quickly rejected to Deerslayer's joy. Hurry Harry, rejected for the last time by Judith, is taken ashore by Deerslayer with the plea that he should try to reach the garrison of soldiers nearby. Deerslayer and Judith open Tom Hutter's chest on the ark, and letters confirm that he was a pirate. After endeavoring to win Deerslayer's love with her frank admission of love for him, Judith realizes that he will not sacrifice his code and his honor and that he will return to the Indian camp for torture and death.
Deerslayer bids farewell on the following morning to his friends (Chingachgook, Hist, Judith, and Hetty) and gives them his final counsel. Chingachgook and he engage in a shooting match with Killdeer, Tom Hutter's rifle given by Judith to Deerslayer, and, after Deerslayer's (expected) death, to Chingachgook. The Mingos are surprised by his honorable return to his sentence of condemnation. Rivenoak, the chief, asks Deerslayer to join the tribe, but is refused. Deerslayer also refuses to marry the widow of the Mingo he killed on his "first warpath." The trial begins with the throwing of knives and tomahawks to unnerve Deerslayer; but he succeeds in seizing one tomahawk, hurling it back at his assailant, and making his escape. Recaptured by the Mingos because the current brought his canoe back to shore, Deerslayer is now tortured by rifle shots fired close to him at the stake and by a fire built at his feet.
Judith appears elegantly dressed, claims she is an important lady with soldiers, and demands Deerslayer's release. Hetty, confused by the events, tells Rivenoak Judith's true identity. Chingachgook and Hist appear individually to challenge the Mingos, but they likewise fail. With all their enemies in hand, the Mingos are triumphant until soldiers from the garrison, guided by Hurry Harry and the shots fired by Deerslayer and Chingachgook on the ark, surprise the Indians and kill most of them.
Hetty has been mortally wounded, and her death saddens all the survivors. After a last plea to Deerslayer to marry her, Judith goes back to the garrison with the soldiers. Deerslayer, Chingachgook, and Hist return to the Delaware territory. Fifteen years later, Deerslayer and Chingachgook return to Glimmerglass with the latter's son, Uncas, and contemplate the great adventure.