The action of the story takes place in 1757 during the French and Indian War (part of the Seven Years' War) in the Adirondack Mountains in what was then the British colony of New York. Three frontiersmen are traveling west to find a new home. The oldest is Chingachgook, the last chief of the Mohican tribe. With him are his son, Uncas, and an adopted son, a white man named Nathaniel Poe, who also goes by the name “Nathaniel Hawkeye”.
Meanwhile, British Army Major Duncan Heyward has arrived in Albany. He has been sent to serve under Colonel Edmund Munro, the commander of Fort William Henry, along Lake George, an important point in the defense of New York against the French in Canada. Heyward has also been given the assignment of escorting the colonel’s two daughters, Cora and Alice, to the fort to join their father. He is a family friend, and in love with Cora, and proposes to her before they leave. She does not give him an answer.
Major Heyward, the two women, and a troop of British soldiers march through the rugged countryside to reach the fort. They are led by a single guide, Magua, a warrior of the Huron tribe. Suddenly, Magua leads the party into an ambush, where many of the soldiers are killed, but Heyward and the women survive. The fight is interrupted by the arrival of Chingachgook and his sons, who kill the enemy warriors while Magua escapes. The major and the women are now stranded and the Mohicans and Hawkeye agree to accompany them the rest of the way. Hawkeye observes that Magua attempted to kill Cora, and asks Duncan about any ties to the Huron. During this trek, Cora begins to form a bond with Hawkeye, and Heyward notices.
When they arrive near the fort, they find it under siege by the French. They enter the fort during the bombardment, and are greeted by Colonel Munro, who asks Major Heyward about the reinforcements. The Colonel admits to Heyward and the others that the fort is about to fall. While there, Cora and Hawkeye share a passionate kiss. Heyward begins to suspect Cora’s attraction to Hawkeye, and erupts in jealousy. In response, Cora finally tells him she will not marry him.
The fort falls, but the French general, Louis-Joseph de Montcalm, paroles the remaining British troops and allows them to return to Albany safely. It is revealed that Magua and his Huron army are allies of the French. In a secret meeting, Magua reveals his hatred for Colonel Munro, and his desire for revenge for the murder of his family.
The following day, Colonel Munro and everyone else march with the British garrison from the fort. In the countryside, Magua and his Huron warriors ambush the British, and Magua kills Colonel Munro. Hawkeye and the Mohicans fight their way through, leading Cora, Alice, and Heyward from the battle, though Magua later captures the Major and the women, and takes them prisoner.
At a Huron village, Magua presents the women and the officer to a sachem, a chief, in hopes of gaining recognition as a war leader. His appeals are interrupted by Hawkeye, who has come to plead for the lives of the prisoners. The sachem rules that while Heyward is to return to the British and Alice is to be given to Magua, Cora is to be burned alive. Hawkeye asks Heyward, who is serving as translator between Hawkeye and the sachem, to take his life in Cora's place. In a final gesture of affection and redemption, Heyward arranges to be executed in Cora’s place. Once Cora and Hawkeye escape, Hawkeye shoots Heyward in the head just as he is about to be engulfed by the flames. Later, along steep mountain trails, Chingachgook, Uncas, and Hawkeye track and ambush Magua’s war party to free Alice. Uncas is killed by Magua and thrown down the mountain. Alice chooses to calmly step off the cliff to her death rather than go to the beckoning Magua. In single combat with Chingachgook, Magua is defeated and killed.
In the end, during a funeral ritual with Hawkeye and Cora, Chingachgook prays to the Great Spirit in honor of Uncas, calling himself "the last of the Mohicans".

Question: Who does Magua kill during an ambush against the British?
Answer: Colonel Monroe