Plot summary

The first king of Aurea leads a futile attack on a dragon (Shohreh Aghdashloo) residing in his realm. All the king's men are killed, leaving the king at the dragon's mercy.Centuries later, Elodie (Millie Bobby Brown), the adolescent daughter of Lord Bayford (Ray Winstone), receives a proposal from Queen Isabelle (Robin Wright) of Aurea to marry her son, Prince Henry (Nick Robinson). King Roderick (Milo Twomey) commands a fleet of ships and carriages full of gold. On her father's urging, Elodie agrees to the marriage to help their impoverished people. Lord Boyford says that their Kingdom is far to the North and encounters harsh winters. He says that their stores are empty, and they will not make it to the next summer without help. Floria (Brooke Carter) is Elodie's younger sister. Elodie travels to Aurea with Lord and Lady Bayford and Floria. Elodie is shown to be an expert in designing mazes.Upon arriving in Aurea, the Bayford's are impressed with the wealth and opulence of the Kingdom. At night, from her chambers, Elodie notices a fire burning at the top of a nearby mountain. Elodie and Henry initially both seem uninterested in each other but begin to bond as they share a desire to travel. Lord Boyford confers with the Queen in private and is offered more gold than he could ever imagine. Yet, Lady Boyford can see that something bothers him when he comes out of the meeting. Elodie's stepmother, Lady Bayford (Angela Bassett), fails to befriend Queen Isabelle. Isabelle insults Lady Bayford by saying that she is the daughter of a rope maker and not of royal blood. Isabelle is clear that this marriage is a transaction, as her family needs a bride and Bayford need money. Isabelle does not even remember Elodie's name and calls her Eloise. Lady Bayford futilely implores Elodie to end the engagement.After the wedding the next day, Elodie and Henry take part in an ancient ritual in the mountains, supposedly to celebrate their union. Isabelle says that when their ancestors first settled on this land, they found the dragon who ravaged their villages. The dragon was the last of its kind, but savage. The King attacked the dragon in its lair and was defeated. Isabelle describes the pact between the first king and the dragon, where he had to sacrifice his three daughters for peace. The King put the duty to his subjects above than the love of his daughters. This sacrifice is commemorated every generation. Following a ceremony where their hands are cut and held together, Henry carries Elodie across the narrow path over the dragon's lair, then throws her into the chasm.Recovering from the fall, Elodie realizes that she is the actual sacrifice. Her cries wake the dragon. Elodie finds many other pieces of jewelry (that didn't belong to her) at the bottom of the chasm indicating that she is certainly not the first one there. As the dragon talks to Elodie, she realizes that the dragon believes she is from the royal Aurean family, as her blood scent has been masked by Henry's blood in the ceremony. Elodie escapes the dragon after it burns her leg and discovers an illuminated cave filled with glowing slugs, which she collects as a light source. Elodie reaches a chamber with the note "Safe Here She Cannot Reach," the names of past victims (Beatrice, Victoria, Artemis, Genevive, Fatima, Carlotta, and many more) and a map carved into the wall. While Elodie is asleep, the slugs heal the burn on her leg.Elodie follows the map, but it leads to a dead end at a high vertical drop on the mountainside. Elodie is distraught that there is no escape from the dragon's lair. She discovers the remains of dead dragon hatch-lings, providing the reason for the royal sacrifices. Elodie surmises that 3 dragon hatch-lings were killed by the first King and hence the dragon was provoked into attacking them. The first King begged for mercy and promised to pay any price. The dragon demanded a royal sacrifice of 3 daughters from their bloodline in each generation to maintain the peace. A rescue party led by Lord Bayford arrives. Lord Bayford is confronted by the dragon and admits that he traded the life of his daughter for gold and the prosperity of his people. But he could not live with the guilt. The dragon kills them, but the distraction allows Elodie to escape the mountain. She takes one of the rescue party's horses and hides under a rock as the dragon burns the surrounding area in an unsuccessful pursuit.The conflagration alerts Isabelle that Elodie's sacrifice has failed, forcing her to kidnap Elodie's younger sister Floria as a replacement. After Lady Bayford rides out and informs her, Elodie returns to the mountain to rescue Floria, who is left alive as bait.Elodie creates a diversion for the dragon to reach Floria. Telling her sister to hide, she confronts the dragon and tries to convince her that they were deceived by the Aureans. The Aureans claim that the King only attacked the dragon to defend his people, but the dragon says that he came unprovoked. Elodie says that by joining their cut hands at the wedding, the blood of the brides and the Aurean royals mingled, making the dragon think of the princesses as Aurean royalty. The dragon refuses to believe Elodie, and then attacks her, but Elodie tricks her into burning herself by spewing fire in front of a rock that deflects the fire back onto the dragon. With the dragon at her mercy Elodie tells her that she has been killing innocent daughters for centuries just like the first King did. Elodie heals both of them with the glowing slugs, thus gaining the dragon's trust and loyalty.Elodie then interrupts another wedding at the palace (After Elodie and Floria, this would be the 3rd princess to be offered to the Dragon in this generation), exposing the Aureans' treachery. Elodie advises the new bride and her family to flee, and the dragon burns the palace with all the Aurean royals and nobles inside. Days later, Elodie, Floria, and Lady Bayford sail home, loaded with supplies and accompanied by the dragon.