Justin, Freddie Highmore lives in the kingdom of Gabylonia and dreams of becoming a Knight of The Valour Kingdom like his grandfather, Sir Roland. After the king’s death, knights are outlawed and replaced by lawyers, a shift that his father Reginald, Alfred Molina—the Queen’s Chief Lawyer—fully supports. Reginald’s disdain for knights colors Justin’s path toward law, even as the boy secretly longs for the old code of courage and honor.
When Justin discovers that Sir Roland’s sword is missing, he decides to embark on a quest to recover it. His grandmother Lilly urges him to seek training at the Tower of Wisdom, a place rumored to shape seekers into true knights. Before he sets off, Justin visits his crush, Lara, Tamsin Egerton, a pampered noblewoman’s daughter who barely notices him. In a moment that feels like a last flicker of luck, Lara offers him a dirty sock as a token of luck—one he vows to return once he has proven himself.
The journey leads to the Broken Eagle Inn, now a fast-food hub, where Justin meets Talia, Saoirse Ronan—a weary barmaid—and Melquiades, David Walliams—a wizard whose talents don’t quite live up to his grandstanding. When Justin steps in to defend Talia from the inn’s bullying guards, Igor and Slamski, Talia’s feelings for him begin to stir. A sense of destiny deepens as Justin realizes the kingdom’s protection has frayed, and a larger threat lurks beneath the surface.
From exile, Heraclio, Mark Strong, the knight who killed Justin’s grandfather, returns with an army of criminals to retaliate against the Queen and Reginald for outlawing knights. The Queen worries aloud that the ban has left Gabylonia exposed, a worry that echoes through the court. Clorex, Antonio Banderas—an armour polisher who seizes armor to pose as a knight—begins operating out of the Broken Eagle, charging patrons for autographs and sowing confusion about who truly deserves the title. Talia, threatened by her boss, is urged to keep quiet as Clorex’s “reputation” draws business to the inn.
Justin finds the Tower and trains with Braulio, Barry Humphries the monk, Legantir, Charles Dance the patient mentor, and Sir Blucher, James Cosmo. Blucher reveals a painful truth: Heraclio stole Justin’s grandfather’s sword after killing him. For the final test, Justin faces a dragon—though dragons are extinct, he must contend with Gustav, a mechanical-winged alligator armed with a flamethrower. The trial goes awry, leaving Justin near fatally wounded. The monks cut training short and send him home, but Blucher lends him his sword, a symbolic passing of the old code.
Back at the Broken Eagle, Justin reconnects with Talia. Igor and Slamski rekindle trouble, but Talia, tired of Clorex’s opportunism and the inn’s shifting loyalties, joins Justin in battle and ultimately quits her job. Yet she learns that Justin harbors feelings for Lara, a revelation that stings with irony.
At Lara’s coming-of-age party, Lara discovers that she has fallen for Clorex, complicating the knight quest that Justin pursues. Heraclio’s men attempt to kidnap Lara for ransom, but Clorex—still playing the knight—drives them away, their mistake foreshadowing the deeper rift between appearances and reality. After a humiliating display as a would-be knight, Justin returns home with Reginald, who remains wary of the path his son has chosen. Clorex then kidnaps Lara, delivering her to Heraclio, reigniting the danger that Justin must confront.
Talia informs Justin of Lara’s kidnapping, and Justin’s resolve hardens: he will rescue her, and Reginald must accept his choice to pursue knighthood. With Melquiades guiding them to Heraclio’s hideout, Justin and Talia locate Lara, and Lara’s feelings toward him shift again in the heat of action. Lara’s admiration for Justin grows as she witnesses his courage, and she also warms to Talia after seeing their teamwork in peril.
Surrounded by enemies, Justin and Talia refuse to back down. Blucher arrives with Gustav, frightening the attackers away, and the duel between Blucher and Heraclio begins in earnest. Talia confronts Clorex, exposing his cowardice and false boasts; she defeats him in a fistfight and rescues Lara. Heraclio wounds Blucher but then duels Justin, who manages to disarm the exiled knight and reclaim his grandfather’s sword. In a climactic turn, Justin sends Heraclio over a waterfall to his death, ending the threat to Gabylonia’s future.
With the danger past, the Queen knights Justin as Sir Justin. Reginald and the Queen resolve to restore the knights to their former place in the realm, recognizing that the kingdom’s safety depends on courage and honor rather than words alone. Lara faints when, instead of proposing, Justin returns her dirty sock in front of the entire kingdom, a moment of comic honesty that underscores the human heart behind the legend. Nonetheless, Justin declares his intention to keep adventuring with Talia, and she accepts with a kiss, sealing a partnership built on trust and shared quests.
Back at their tower, Braulio, Legantir, and Blucher erect a statue of Justin beside his grandfather Sir Roland and unveil a new hall dedicated to the knights-to-be, a hopeful omen for Gabylonia’s future and the next generation of heroes.
