The film begins with a woman, Sintel, being attacked while traveling through a wintery mountainside. After defeating her attacker and taking his spear, she finds refuge in a shaman's hut. He asks her why she's travelling, and she confesses she's looking for a dragon, leading into a flashback. Sintel was a homeless loner, looking for food when she discovered an injured baby dragon. She nursed him back to health and named him Scales, the two quickly formed an emotional bond. One day while Scales was flying he was captured by an adult dragon. Determined to get him back, Sintel began the long and dangerous journey that led her to the shaman's hut.
She's ready to give up, when the shaman tells her they're in dragon lands, showing the glyph on the spear as proof. She finds the tree pictured on the spear and near it, a cave with the adult dragon and his baby. The baby runs away upon seeing Sintel and the adult dragon attacks. After a brief battle, the adult dragon pins Sintel to the ground, but freezes when he sees her face. Sintel takes advantage of this and stabs the dragon in the heart. As she's about to land the killing blow, she then notices the scar on its wing is exactly the same as her old friend's. Sintel discovers in a moment of horror that she has just killed Scales.
Scales bleeds out rapidly, and Sintel stares in shock at her reflection in a pool of blood. It is revealed that she is significantly older than she has appeared throughout the film. She has many gray hair, worn and wrinkled skin, and several scars on her body. The long search for Scales had lasted several years and she had never realized that during all these years, Scales would've grown up. Her single-minded quest to get back her friend and to take revenge from the large dragon who took Scales away contributed to her mistaking Scales as the large dragon. The cave begins to collapse as Scales gives his last breath, and Sintel runs for the entrance.
After mourning over the friend she killed, Sintel leaves, heartbroken. Scales' baby, having nowhere else to go, follows her.