In the first years of the 15th century, England is in the middle of a civil war. Powerful rebels have assembled against King Henry IV in an attempt to overthrow him. They have just suffered a major defeat at the Battle of Shrewsbury, but several rebel leaders--including the Archbishop of York, Lord Mowbray, and Lord Hastings--remain alive and continue to wage war against the king. King Henry, aging prematurely because of his anxiety over the war and over his oldest son, Prince Hal, has recently become very ill.
Prince Hal has spent most of his teenage years raising hell in taverns with a group of lowlife friends. His closest friend and mentor is Falstaff, a jovial, aging, witty criminal. Falstaff and some of Hal's other friends have won wealth and power at the Battle of Shrewsbury. We watch Falstaff, now an army captain, drink in a London tavern and travel around the countryside to recruit young men to serve in the upcoming battles. Prince Hal, meanwhile, knowing that he will have to take the reins of power when his father dies, has vowed to change his ways and become responsible. He has started to spend less time with his old friends.
The rebel leaders gather their forces to battle the king at the Forest of Gaultree. They are disappointed when the powerful Earl of Northumberland does not offer soldiers to support them. (This is the second time he had refused to offer aid; the first time, at the Battle of Shrewsbury, his refusal led to his son's death in battle.) Prince John, the king's second son, leads the king's army to meet them at the forest. Prince John says he will agree to all the rebels' demands, but as soon as the relieved rebels have sent their soldiers home, he arrests them for treason. The rebels protest this injustice, but the prince has them executed.
Meanwhile, at his palace in London, King Henry IV grows increasingly sick. He is worried about what will happen when his wayward son becomes king. Prince Hal comes to the palace; his father gives him a tongue-lashing, and Prince Hal, in an eloquent speech, vows that he will be a responsible king. His father forgives him and then dies. Prince Hal, now King Henry V, tells the Lord Chief Justice, the highest law official in England, that he will now view him as a father figure.
After the rebels have been executed, Hal is formally crowned King Henry V. Falstaff and his companions come to London to greet him, but in the middle of a public street, the king rejects Falstaff, telling him he must never come within ten miles of the king or court again. He may have a pension, but the king will have nothing more to do with him. Then the young king goes to court to lay plans for an invasion of France.