The film commences in 1361, where the infant Princess Margrete of Denmark is an unwilling witness to the violent consequences of her father, King Valdemar IV's victory during the Battle of Visby. Fast forward to 1402, and we see Margrete, now a formidable queen regnant, traversing the breathtaking Hardangervidda plateau in Norway alongside her loyal retinue. Accompanying the journey is a caption revealing her significant achievement: she has unified Denmark, Norway, and Sweden under her rule, governing through her adopted son, King Erik. This historic moment has ushered in an era of unprecedented peace across the Nordic countries, a rarity that hasn't been seen for centuries.
As she arrives at a majestic fjord, Margrete addresses a gathering of the leading Nordic magnates. She emphasizes the peace that the Kalmar Union has brought over the past decade but insists that it is now essential to establish a Union army. In a bold announcement, she reveals plans for Erik to be betrothed to Princess Philippa, the daughter of King Henry IV of England. Margrete explains that a robust military force is vital for securing a military alliance with England, which would serve to deter the looming threats posed by German forces, particularly the Teutonic Order, especially after their recent seizure of the Swedish island of Gotland. Each of the magnates agrees to contribute troops to this noble cause.
In a strategic move, Margrete enlists the help of Roar, a pirate from Kullen in Scania, tasking him with blockading Gotland. She also takes under her wing Astrid, a Swedish girl who has been rescued from a German vessel, bringing her to Kalmar Castle in Sweden. Here, she confides in her friend and financial backer, Peder Jensen Lodehat (Søren Malling), the Bishop of Roskilde, about the fruitful outcome of her travels.
Months later, Margrete gathers the magnates again in Kalmar to welcome Princess Philippa and Sir William Bourcier, an English lord charged with negotiating the terms of the marriage agreement. During a celebratory feast, Asle Jonsson (Bjørn Floberg), leader of the Norwegian Council, brings disconcerting news from Graudenz in Prussia: he believes he has seen King Oluf, Margrete's son, who has been presumed dead for 15 years. Despite her assurances that Oluf is no longer alive, Asle is adamant, claiming that the Man from Graudenz is indeed "my King" and he has brought him to Smedby. Margrete suspects that this so-called 'false Oluf' might be part of a devious plot devised by the Teutonic Knights and, needing Norway's pledge of troops, she orders Asle to bring the man to Kalmar for interrogation.
As rumors swirl during the feast, Margrete is faced with a rising tide of mistrust, especially after Astrid overhears troubling stories about Erik being Margrete's sister's grandson and whispers regarding Margrete's alleged involvement in Oluf's death years before. Constrained by her role, Margrete reluctantly declares that the pretender's claim is an act of treason against the Union, assuring everyone that he will receive a fair trial.
However, negotiations with Bourcier soon hit a roadblock due to the sudden question surrounding Erik's legitimacy as king. While the Man from Graudenz stands accused in handcuffs, claiming to be Oluf, Margrete remains skeptical yet resolute: "My son died," she responds coldly. The man states that he was meant to have been killed by Esge Vind, a retainer who ultimately spared his life but allowed him to be captured by the Germans. As this shocking tale unfolds, Danish Council leader Jens Due (Thomas W. Gabrielsson) dismisses the man's claims as mere fantasy, while the Norwegian magnates rally behind Asle's insistence that they are in the presence of their legitimate king.
As the drama intensifies, Margrete grapples with her predicament. If the Man from Graudenz is truly Oluf, it could mean Erik’s throne is in jeopardy. As tension mounts, Peder urges her to execute the pretender swiftly to maintain peace among the three realms, while Bourcier warns that negotiations would end if Erik’s status remains unresolved. Amidst the chaos, Margrete’s growing dialogue with the Man from Graudenz leads her to ponder whether he truly might be her long-lost son. Doubts further deepen when she learns that none of her advisors were present during Oluf's burial, nor did they open his coffin due to fears of plague.
In her quest for the truth, Margrete instructs her Swedish retainer Jakob Nilsson (Simon J. Berger) to seek out Roar for additional insights into this complex situation. She proposes a desperate solution: if the Man from Graudenz renounces his claim as Oluf, she will allow him to live. However, he remains obstinately unwilling to claim falsehood. Meanwhile, Bishop Peder argues that as long as the pretender lives, he poses an ongoing threat to their unity.
With time running out, Margrete experiences a sudden realization: the Man from Graudenz’s assertion of an assassination order may be crucial. She confronts Peder, who ultimately confesses his role in this tragic affair, having conspired to eliminate Oluf for what he deemed the greater good. He explains that Oluf’s temperament would never have been accepted by the Swedes, thereby justifying his drastic actions to secure Margrete's reign over Denmark-Norway and subsequently Sweden.
Convinced of the man's identity as Oluf, Margrete's resolve is tested when Erik, desperate to maintain his grip on power, produces a false witness who claims to have taught the imposter how to mimic Oluf. The court is swayed, and Oluf is found guilty of treason, condemned to death despite Margrete and the Norwegian magnates’ desperate protests. The Danish and Swedish factions rally behind Erik, compounding Margrete’s isolation.
That fateful evening, Margrete contrives a plan to rescue Oluf with the help of Asle. Yet, things take a dramatic turn when Jakob Nilsson and Roar return with alarming news: the Teutonic Order is preparing to invade mainland Sweden, deliberately manipulating Oluf's situation to disrupt the fragile alliance with England and jeopardize the Kalmar Union. Confronted with this dire threat, Margrete makes a heart-wrenching decision—she betrays her son, leading to his recapture. Although she manages to plead for Asle’s safety, Oluf is publicly executed by fire, casting a haunting shadow over Margrete as she puts the greater good of the Union above her personal sorrow.
In the end, the film closes with a poignant reminder: the legacy of the Kalmar Union endured for an additional century following Margrete's death, underscoring her pivotal role in forging lasting connections among the three Nordic nations, an affinity that resonates even to this day.
