The French-Indian war is in full swing. The French are trying to overtake the English fort William Henry. They have the Huron and the Iroquois on their side, so the forests are extremely dangerous for English travelers. Duncan Heyward must escort the Munro sisters from Fort Edward to Fort Henry, where their father is. They have an Indian runner, Magua, who is their guide. When in the forest, they are approached by the musician David, who has heard that they are going to William Henry and asks if he may join them. Duncan is reluctant, but Alice convinces him to let David stay with them. As they walk, someone watches them and traces their footsteps. It is the Mohican Uncas. The author switches to a scene nearby, where Hawkeye and Chingachgook are conversing about the different beliefs of whites and Indians. Uncas returns to them and alerts them of Huron hiding in the woods. Chingachgook hears the approach of the travelers. He asks Hawkeye to speak to them in their native language. Upon meeting Duncan and learning of their destination, the scout tells him that they are completely off course. Hawkeye believes their guide has led them astray on purpose. Looking upon Magua's countenance, his belief is confirmed. Hawkeye wants to shoot him, but Duncan will not permit it. He tries to capture Magua himself and fails. The scout shoots the Huron chief, but only hits his shoulder. The foresters converse, and decide to take the travelers out of harm's way and become their guides.
The group passes the night in a cave that they reach by canoe. David sings for all of them, which brings tears to Hawkeye's face. A strange sound is heard. After going outside, Duncan realizes it is a horse in peril. Uncas is dispatched to try and stop the noise. He returns safely. The women sleep while the men stand guard. At daybreak, they are ready to leave, but a shot rings out and wounds David. Uncas and Hawkeye slay two of the men. Duncan wrestles with a third but has to be rescued by Uncas. There is a sniper in a tree. After a bit Hawkeye manages to kill him with his rifle. Uncas goes to the canoe to get more gunpowder, but it has been stolen. Cora urges the foresters to depart and get help from her father. Somewhat reluctantly, they heed her good advice. The travelers hide in the deepest recesses of the cave. Eventually they are pulled out by the Huron party, led by Magua. They are marched out of the cave as prisoners. Magua desires the blood of Hawkeye. Upon finding that he has escaped, he is quite angry. The tribe stops to rest. Magua asks to speak to Cora. He says he will free the other travelers if she will become his wife. Cora is repulsed and refuses. Duncan and Alice agree with her decision. Magua decides that they should all die. Duncan jumps upon a warrior and is almost killed, but a shot rings out and kills the Indian. The foresters descend to help them. Chingachgook battles with Magua as the other two kill his comrades. Magua pretends to be dead and then manages to roll over a precipice onto a hill. He runs away.
The foresters lead the group away, stopping briefly for dinner. They walk a bit more until they reach an old war building. Many Mohicans died there, and Chingachgook and Hawkeye fought together in the battle. The old Mohican is the sentinel as everyone else sleeps. A noise is heard. Some Huron approach the building, but being scared of the dead, they will not go inside. The group stays a bit longer until Chingachgook decides it is time to leave. They are getting very close to William Henry. Duncan manages to deceive a French officer into believing that they are on his side. By the time the deceit is discovered, they are close enough to the fort to dodge the shots. The door opens and Munro comes out to embrace his daughters.
In the fort a few days later, Duncan walks about, wondering how they can keep fighting with such inadequate manpower. Reinforcements from Webb are the only hope. Talking to Munro, he learns that Montcalm has asked for a meeting. Munro wants Duncan to go in his place. A letter to Munro has been intercepted, and he wants Duncan to see if he can get any information about it. Duncan attends the meeting, but only learns that the French know how few men the English have. During this conference, it comes out that Duncan is in love with Alice. Another meeting is arranged between both armies. Montcalm and Munro advance to the front. Montcalm urges surrender as he hands Munro a letter, detailing Webb's inability to send reinforcements. At first Munro will not hear of it, but when he hears how fair the terms are, he agrees and signs a treaty. Meanwhile, Magua is furious at the proceedings. He tells Montcalm that his warriors have no scalps, while the white men become friends. During the retreat from William Henry, the Huron attack, slaughtering tons of innocent people. Magua spies Cora in the chaos and asks her again to be his wife. When she refuses, he grabs the unconscious Alice and throws her upon a horse. Cora runs after them and is made to follow Magua. Seeing this from a distance, David joins the sisters.
Later that day the foresters return with Munro and Duncan to survey the damage and to try to detect Magua's trail. They pass the night in the old fort before setting out the next day. An Oneida shoots upon them and is caught by Uncas. Apparently there are neighboring tribes involved in this conflict. The next day they travel by canoe. They come under the fire of Huron, who paddle after them. Through the rifle of the scout and the speedy rowing of the Mohicans, they manage to escape and lose the Huron canoe. Once on land, they manage to find the correct trail and stand within view of the Huron village. A tall stranger is just outside the bush. Hawkeye moves to pounce on him, but laughs as he realizes that it is the musician David. David relates that Cora is with a neighboring tribe of Delaware who are descended from the Mohicans. Alice is in the Huron village. David, owing to his beautiful voice, is allowed to walk around as he likes. Duncan insists on going to the village with David to see if he can rescue Alice. Chingachgook paints him in peace symbols. Munro and Chingachgook will go to the Delaware to see if Cora may be released. Hawkeye and Uncas will stay in the forest. Once in the village, Duncan manages to convince the council that he is a doctor sent by the Canada father, who wants to make sure that they are healthy. The Indians are impressed with his presence and believe he can cure the sick wife of a young warrior.
Suddenly there is a big hullabaloo outside the meeting house. Duncan is horrified to see that Uncas has been caught. When taunted by the Huron woman, Uncas replies that he only came into the village to seek the coward that would not fight him face to face. The tribe is very displeased with this young man, and decides that his name will be mentioned no more. The young man then commits suicide, and Uncas is taken into the meeting lodge. Duncan sits with the group, but to his horror Magua enters, having returned from a day of hunting. The paint seems to disguise Duncan well enough. Magua spies the prisoner and is absolutely delighted. When the tribe realizes who this is, they rejoice as well. Magua decides that he will have to try and sleep the night. Duncan is led the cave of the sick woman. David is there with a circle of female attendants, but they leave as soon as Duncan's guide shoos them from the cave. A bear seems to have followed the major inside. Once they are along, a mask comes off and the face of the scout appears.
Ambling about, Hawkeye discovers that Alice is just over the cave wall. Duncan rushes to see her, says he is going to rescue her. Unfortunately Magua walks in on them. He is about to leave to get the rest of the tribe, but Hawkeye, still in costume, hugs him tightly so that Duncan is able to bind and gag him. Alice is put under a blanket, and Duncan carries her out, telling the people outside the cave that he is taking the sick young woman to the woods for more healing. He tells them not to go inside, lest they encounter the evil spirit from her body. Once in the forest, Hawkeye instructs them to find refuge in the neighboring Delaware tribe. He returns to the village for Uncas as a bear. David is able to convince those guarding the young Mohican that they are there to take the courage of Uncas. Inside, Hawkeye reveals himself. Uncas wants to run to the Delaware tribe, but Hawkeye knows he cannot keep up. Uncas therefore decides to stay with the scout. Uncas puts on the bear costume. David agrees to sit in the lodge in place of the captive. Hawkeye puts on his clothes, and escapes to the forest from under the noses of the Huron.
When all deceit is discovered, the tribe is furious. They leave to meet the Delaware. Magua goes forth and talks to their leaders, asking if strangers have been spotted. While they talk, the escaped prisoners are discovered. They are taken into the middle of the village, into a circle that comprises everyone. When Hawkeye's identity is revealed, he is bound. Uncas comes forward. At first the tribe is angry with him for infiltrating their village, but when they see the tattoo on his chest, they realize that he is a Mohican and rejoice that he has returned. Tamenund agrees to let everyone go except for Cora, who must go with Magua. She leaves with her Huron captor. At sunset Uncas readies his people to fight the Huron and steal her back. A battle commences, in which the Huron lose terribly. Magua is forcing Cora to run, but she stops at one point and will not move. He offers her his wigwam or his knife. She raises her eyes to God. Uncas reaches them and struggles with Magua. A Huron kills Cora. Furious, Magua drives his tomahawk into Uncas. Uncas manages to kill Cora's murderer before he dies. Magua tries to escape but the scout is finally able to shoot him. The next day, funeral services are held. The story becomes a legend.