The film opens with an animated overview of the Arthurian legend, quickly getting viewers up-to-date on King Arthur; his evil sister, Morgana; the wizard Merlin; the Knights of the Round Table; and the importance of the magical sword Excalibur. The action then switches to modern-day England, where 12-year-old Alex (Louis Ashbourne Serkis) saves his best friend, Bedders (Dean Chaumoo), from their school's two biggest bullies: slightly older Lance (Tom Taylor) and Kaye (Rhianna Dorris). After running away from the bullies, Alex ends up falling into a construction site and sees a dusty old sword stuck in a stone, which he manages to dislodge. The appearance of Excalibur brings Merlin (Angus Imrie), in teen form, to Alex's town. The odd, lanky teen explains that Alex is the new true king – and that he will need to rally a group of fighters to defeat the wicked Morgana (Rebecca Ferguson), who's gaining strength to resurface and reclaim not only the sword, but all of Great Britain, as her birth right.

Director Joe Cornish gives Arthurian legend a modern, crowd-pleasing twist in this version by choosing a kind, courageous "everyboy" to be the once and future king. Ashbourne Serkis (actor-director Andy's youngest child) plays Alex as an earnest, brave 12-year-old who can't quite believe that the magical sword belongs to him. The diverse group of kids who end up battling evil has a certain kinship to the ensemble in Cornish's clever (and decidedly more grown-up) debut, Attack the Block – except, here, instead of aliens, these kids are trying to defeat a medieval sorceress who's trying to take over the United Kingdom.

The film is slightly longer than it needs to be, but Alex's drive to do what's right is charming, and the young Merlin's quirkiness (don't be surprised if young viewers attempt his constant snapping and clapping) is endearing. Patrick Stewart makes a few appearances as the "old" version of Merlin, adding an extra layer of legitimacy to the proceedings. The sword training and fight sequences are just violent enough to feel edgy, but they're not so dark that older elementary-aged viewers won't be able to handle them. Kids will be delighted by the young knights' adventures, and parents will appreciate how the Arthurian code promotes truth-telling, honouring loved ones, and perseverance. There's also an admirable theme of turning rivals (in this case, the bullies) into allies with empathy and kindness. In a world with too many divisions, that's a message that everyone should internalize.

– Compilation