In a jousting tournament set in 14th-century Europe, the story follows a group of squires: William Thatcher, Roland, and Wat, who are devastated by the death of their master, Sir Ector, just before he could claim victory. Struggling with their newfound uncertainty, William decides to don Sir Ector's armor in a bold attempt to impersonate him and claim the tournament's prize for himself.
Despite the strict rules that only allow nobles to compete, William's determination propels him to pursue further victories. While Roland and Wat are tempted to walk away with their earnings, William persuades them to assist him in refining his skills for the noble competition ahead. As they journey, they meet the destitute yet clever young Geoffrey Chaucer, who agrees to help William forge a patent of nobility, allowing him entry into the tournament under the name "Sir Ulrich von Liechtenstein" from Gelderland. However, their path is not straightforward; William must confront Simon the Summoner and Peter the Pardoner due to Chaucer's gambling debts, ultimately promising to pay their claims to secure Chaucer's release.
As the tournament unfolds, William faces unexpected challenges, including damage to his armor, pushing him to convince Kate, a skilled female blacksmith, to repair it for him without charging. His prowess shines during the sword event, allowing him to clear Chaucer's debts. In the jousting rounds, William's skills lead him to engage with Sir Thomas Colville, who ultimately relinquishes his tournament participation after being injured by William. Their mutual respect is solidified in a ceremonial pass that preserves Colville's honor.
Throughout the competition, William becomes enamored with Jocelyn, a noblewoman who captures his heart. However, he faces fierce rivalry from Count Adhemar of Anjou, who not only competes in the jousting matches but also vies for Jocelyn's affections. Their rivalry climaxes in a final joust where William, despite putting his best foot forward, initially falls to Adhemar. Humiliated yet resolute, William vows revenge against Adhemar, who taunts him with the phrase, >"You have been weighed, you have been measured, and you have been found wanting."
With Kate now firmly part of William's circle, she crafts lighter armor to support his quest. During subsequent tournaments, both William and Adhemar find themselves against Sir Thomas Colville, eventually revealed to be Prince Edward, the heir to the English throne. To preserve the prince’s safety, Adhemar opts to withdraw, while William boldly chooses to joust, earning Edward’s admiration.
Amidst these challenges, Adhemar is called to battle, allowing William to amass victories in his absence. To prove his devotion to Jocelyn, William complies with her request to lose deliberately, only to eventually change his course and secure the tournament win.
As they head to London for the World Championship, William reflects on his past, having forsaken his father to become a knight under Sir Ector, with the desire to "change his stars". However, Adhemar’s arrival in London complicates matters as he seeks to claim Jocelyn's hand in marriage. As the tournament progresses, William excels but remains haunted by his humble beginnings and the truth about his identity.
When the time comes, Adhemar exposes William’s true origins, leading to William's arrest. However, William's friends bravely protect him from the outraged crowd. Just when tensions peak, Prince Edward reveals himself to advocate for William, praising his honor and commitment, and consequently, knights him as "Sir William". This declaration is made with the authority of the Prince, securing William’s noble status beyond question.
In the fateful final match against Adhemar, William faces immense odds as he is injured by an unfair attack with an illegally sharpened lance. As he struggles against Adhemar, he calls upon his friends and, with the show of true spirit and perseverance, prepares to tilt. Even in his weakened state, he has Wat strap the lance to his arm, symbolizing the support of true friendship.
When the final moment arrives, William confronts Adhemar with fierce determination in front of his father and Jocelyn. With a triumphant shout, he strikes Adhemar down, echoing the very words of mockery that Adhemar once used against him, "weighed, measured, and found wanting." With this noble victory, William achieves glory, leaving behind a legacy that Chaucer humorously muses deserves to be chronicled in a grand tale. In this pivotal moment, friendships are solidified, love triumphs, and the spirit of chivalry comes alive, marking an unforgettable journey of a squire striving to become a knight.
