It is 1781, and the war for American independence is in its sixth bloody year. In Virginia, the patriot forces of the Marquis de Lafayette meet the army of British general Lord Charles Cornwallis near Green Spring Farm. On one side of the field are two brothers from Massachusetts, Daniel and Joshua Brattle. On the other side is Sergeant Tom Martin of the British 1st Light Infantry. Each is confident of victory, but it is Cornwallis who prevails, sending Lafayette's army reeling back in defeat.

Joshua Brattle is wounded, and Daniel takes him to a farmhouse where he meets Catherine Seawell and her younger sister Abigail. The women agree to help Daniel care for his injured brother. Cornwallis marches to the tobacco port of Yorktown, which he fortifies as a naval base on the orders of his superior, Sir Henry Clinton. Cornwallis worries that the war can no longer be won. Meanwhile General George Washington knows he needs to win a key victory before the winter of 1782. He conceives a complicated plan to trap Cornwallis in Yorktown by both sea and land, and so force his surrender.

With the defeat at Green Spring, Daniel no longer believes independence possible. He and Catherine, who opposes the war, grow closer over the course of Joshua's long recovery. It is only at Joshua's urging that Daniel agrees to return to the Continental Army.

Catherine is reunited with her missing cousin John Chester, who has joined the cavalry of Tarleton's British Legion. John takes the sisters to Yorktown. The re, the allied armies of Washington and French General Rochambeau at last arrive in Virginia. The French navy has prevented the British from reinforcing or evacuating Cornwallis, who is now trapped.

Daniel Brattle accepts a promotion to captain and vows to do his duty to the last. The Americans and French march on Yorktown and establish siege lines. Hoping for reinforcement from General Clinton, Cornwallis prepares to wait. He sends his cavalry to forage the countryside, and John Chester sees his first action in a battle to defend a supply train from French cavalry.

The turning point comes when the Americans storm two British redoubts. The victory gives Daniel hope, but convinces Cornwallis his position is now untenable. The British commander makes one last attempt to escape the trap, but when it fails, he agrees to surrender. Starving, sick and dispirited, the British march out of Yorktown and lay down their arms. Sergeant Tom Martin of the British 1st Light Infantry is embittered, believing the British generals and politicians have failed the redcoat soldiers.

Daniel meets with Catherine and offers marriage, but she tells him she will not marry him as long as the war continues. She and Abigail will go to New York as Loyalist refugees.

General Washington hosts a dinner for his British counterparts, now on parole. Washington is concerned for the future, with what his struggling new nation will achieve after this victory. Daniel pines for Catherine, but Joshua explains to his younger brother that here is the long-awaited victory that might convince the British to recognize American independence.