In an unnamed Swedish city, ten year-old Karl Lejon has found out that he is going to die from an unspecified pulmonary disease (most likely
tuberculosis). His adored big brother, 13-year-old Jonatan, calms him down and tells him that in the afterlife, all men will go to a land known as Nangijala. One day, a fire breaks out in the Lejon home. Jonatan takes Karl on his back and jumps out of the house's window to save him, but dies himself in the fall. Karl is crestfallen over his brother's death, until, just before his own demise, he receives a sign which allays his fears of death, and when he wakes again, he finds himself in the Cherry Valley of Nangijala, where he is happily reunited with Jonatan. Karl is introduced to the denizens of the valley, particularly Sofia the dove-keeper, Hubert the hunter, and Jossi, a landlord, and assumes the surname Lionheart along with his brother. Despite first appearances, not all is truly at peace in Nangijala. The adjacent valley, the Thorn Rose Valley, is suppressed by a tyrant named Tengil, his army and a female dragon named Katla, who is controlled by Tengil through a
trumpet. The people of the Cherry Valley, led by Sofia, are aiding the resistance movement in the Thorn Rose Valley, but they know someone from the Cherry Valley is helping Tengil, as Sofia's white doves, which transport secret messages between the valleys, are being shot. Soon after Karl's arrival, Jonatan leaves to assist the Thorn Rose people. Prompted by a nightmare in which he sees Jonatan in danger, Karl follows him in the middle of the night, but while hiding in a cave, he witnesses a clandestine exchange between two of Tengil's soldiers and Jossi, who has turned traitor to his people. Soon after Jossi leaves, Karl is discovered by the soldiers and taken to the Thorn Rose Valley after claiming that he lives there with his grandfather. After arriving at a village, Karl throws himself into the arms of the first old man he encounters when he sees white pigeons with him, and surprisingly the old man - by the name of Mattias - takes him in without question. It turns out that Mattias is part of the Thorn Valley resistance and a friend of Jonatan, who is hiding in his house. Jonatan, a hero among the Thorn Rose Valley people, is intent on freeing Orvar, the leader of the Thorn Valley resistance movement who is kept in the cave of Karmanjaka near the Karma Falls, where Katla dwells, with his release sparking the long-anticipated final uprising against Tengil. The Lionheart Brothers soon depart for Karmanjaka and manage to release Orvar moments before he is to be collected and fed to Katla, but their escape is soon discovered. They ride back as fast as they can towards the Karma Falls, but the pursuing soldiers start overtaking Karl and Jonatan. Karl throws himself off the horse and hides so that Jonatan and Orvar can escape, but soon afterwards he encounters Sofia and Hubert, who are being led into a trap by Jossi. Karl denounces Jossi as the traitor, and while trying to escape by boat, Jossi is carried by the river's current to the Karma Falls, where he perishes. The Thorn Rose people rise and engage Tengil's forces in battle, but Tengil calls Katla, who begins to decimate the rebels' ranks, including Hubert and Mattias. Jonatan manages to snatch the trumpet from Tengil and bring Katla under his control, compelling her to kill Tengil. Considering Katla an ever-lingering danger despite her current docility, the people decide to get rid of her once and for all, and Jonatan and Karl volunteer for this task. They lure the dragon to Karmanjaka, where they intend to seal her inside her cave to be weakened by starvation. While navigating the treacherous path, Jonatan loses the trumpet, which frees Katla from his control and drives her into chasing them. The Lionheart Brothers barely escape with their lives when an ancient
lindworm, Karm, suddenly rises from the waters and engages Katla in mortal combat, which ends with the two monsters killing each other. Jonatan and Karl set up a camp for the night, and Jonatan explains that during their flight he was burned by Katla's fire and that he will get paralyzed as a result, and he does not want to live like that. When Jonatan can move only his arms, he tells Karl about the land that lies after Nangijala called Nangilima, a land of light where there are only happy adventures. Karl does not want to be separated again from his brother, so he carries him on his back to a cliffdrop. Karl makes the jump, vowing never to be afraid again, but is cut off as they reach the bottom of the gorge. Then the narrative jump-cuts to Karl crying out jubilantly: "Oh, Nangilima! Yes, Jonatan, yes – I see the light! I see the light!" ==Writing process==