Living harmoniously in the Viking dragon utopia of Berk, Hiccup now serves as chief, with his loyal dragon Toothless by his side. Their efforts to rescue dragons and bring them to Berk have led to overcrowding and the village becoming a target for dragon hunters. When a new threat emerges in the form of the notorious dragon hunter Grimmel, who seeks to capture Toothless and eradicate the Night Fury species, Hiccup decides that the only way to protect their dragons and way of life is to find the "Hidden World," a fabled dragon sanctuary that his late father Stoick once told him about. Determined to keep their dragons safe, Hiccup, Astrid, and their friends embark on a quest to find this mythical place. Meanwhile, Toothless becomes enamored with a wild and elusive Light Fury.

As Hiccup's search for the Hidden World intensifies, the inhabitants of Berk begin their journey to a new home to escape Grimmel's relentless pursuit. Along the way, Hiccup must face the challenge of growing up and becoming a leader worthy of his father's legacy, while also dealing with the complexities of his relationship with Astrid. The bond between dragons and humans is tested as they discover that the world is much bigger than they thought, and they must confront the hard questions about freedom and belonging.