Guided by the displaced Huron warrior Magua, four people — Major Duncan Heyward, Psalmodist David Gamut, and Alice and Cora Munro — strike through the wilderness forest for Fort William Henry, which is besieged by the French near Lake George. Led astray by Magua, they encounter the white woodsman Hawkeye and his two Mohican companions, Chingachgook and Uncas, whereupon the villainous Huron escapes.
Traveling to the safety of the caves at Glenn's Falls, the party is attacked by Indians early the next morning. Running out of munitions, the three woodsmen escape downriver for help, but the others are captured and taken away by a splinter group of warriors headed by Magua. After a long journey, the Huron coldly proposes to Cora, whose refusal brings an attack upon the captives, who are saved by the sudden arrival of the three woodsmen. All the Indians are killed except Magua, who gets away again.
Leading the party of protagonists through narrow escapes from Indians and then besieging Frenchmen, Hawkeye brings them to a mountainside vantage point overlooking the fort. During the trip, a quiet interest develops between the young Uncas and the brunette Cora, while Heyward shows a deference toward Alice. With difficulty finding their way through the heavy morning mists and the omnipresent French, the seven, hotly pursued, finally reach the fort, where Commander Munro recognizes the voice of his daughter Alice and opens a sally-port for them. Heyward leads a repulse of the pursuing Frenchmen.
With the passage of days, a parley is held, and, since General Webb is sending no help, Munro agrees to surrender. Meanwhile, Heyward learns that Cora's darkened aspect lies not only in a brooding nature but also in the fact that she is part black. During the planned withdrawal of the English forces, the Indians begin a bloody massacre, and Magua once again escapes with the two girls and Gamut.
Three days later, the three woodsmen, Munro, and Heyward go north of the lake and across the country in pursuit. When Uncas is captured by the Hurons, Hawkeye effects his escape and Alice's through disguise and all head for the Delaware village where Cora is held captive. Magua follows and demands his prisoners. Uncas reveals himself as a chief to the patriarch Tamenund, and Magua is allowed his only rightful prisoner, Cora, though the protagonists and the Delawares vow to follow and regain her freedom. Coming out of hiding in a beaver pond, Chingachgook and Munro join the ensuing battle, in which the Hurons are defeated. Nonetheless, Magua and two warriors escape with Cora through the nearby caves and up a mountainside. Finally cornered by Hawkeye, Heyward, Gamut, and Uncas, the Hurons give defiance and in the fighting Cora, Uncas, and Magua are killed.
The next day is one of mourning for the Delawares. Cora and Uncas are buried side by side, and all the white characters except Hawkeye leave. When Chingachgook states that he is now alone, Hawkeye grasps his hand and declares that such is not so. At the same time, Tamenund sadly comments upon the worsening historic plight of the American Indians and particularly upon the tragically accomplished demise of the wise and noble race of Mohicans.