A brilliant green comet streaks across the sky above Pixie Hollow, awakening a mysterious creature hidden within a cave. Fawn (Ginnifer Goodwin) is tenderly caring for a baby hawk named Hannah and seeks a wagon from Tinker Bell (Mae Whitman) to transport her into the forest where she can learn to fly and join her flock. Tink warns Fawn that hawks are predators to fairies, to which Fawn retorts that only adult hawks pose such a threat. After covering the baby hawk with blueberries, they set off, but are quickly interrupted by the other fairies. Rosetta (Megan Hilty) attempts to help by applying pixie dust to the wagon, inadvertently revealing Hannah. Panic ensues among the fairies as the sound of Hannah's cheeping attracts adult hawks. While the scouts work to fend off the predators, Nyx (Rosario Dawson) saves Iridessa (Raven-Symoné), but tensions rise as Queen Clarion (Anjelica Huston) arrives to remind Fawn to think rationally about her choices. Ultimately, Fawn releases Hannah, who takes flight.
The following day, as Fawn teaches baby bunnies to hop, she hears an ominous growl and sets off to investigate. This leads her to the cave, where she encounters a creature she has never seen before, struggling with a thorn stuck in its paw. When she tries to help, it roars, startling everyone. The scouts, curious about the roar, are directed to Fawn for answers. As the creature emerges from its cave and begins stacking rocks, Fawn decides to assist. Using a vine, she lifts a rock high, allowing the creature to successfully remove the thorn. In gratitude, the creature constructs a tower from rocks, adhering them with its spit. Fawn eagerly returns home to gather a sketchbook, but Nyx confronts her about the roar. Fawn deliberately feigns ignorance, but she continues her secret study of the creature, whom she names Gruff after he inadvertently causes a commotion with his building activities.
As the days go by, Gruff's towers begin to take shape. Fawn is determined to show her friends the friendly giant, believing he means no harm. Yet, as a storm approaches, the legend of the NeverBeast unfolds—a creature that awakens once every thousand years to build structures tied to the seasons, only to unleash a devastating lightning storm on Pixie Hollow. Despite Nyx’s fears, Fawn believes in Gruff’s goodness, but when lightning strikes and chaos ensues, the fairies must confront the legend's darker implications.
Fawn’s connection with Gruff deepens as she learns of his true purpose: to gather lightning from the four towers to protect Pixie Hollow. Conflict arises when Nyx and the scouts attempt to stop him, leading to misunderstandings and chaos. Fawn courageously navigates the treacherous storm to rescue Gruff, revealing the misunderstood creature's true nature just in time to save Pixie Hollow from destruction.
In an emotional climax, Gruff sacrifices himself to harness the storm’s power, restoring balance to their world. With the dawn of a new day, as Gruff helps to rebuild, the fairies are filled with mixed emotions. They realize this remarkable creature must return to hibernation, having completed his ancient duty. As Fawn bids farewell, she expresses her love and gratitude, promising that their bond will endure, even as Gruff falls into a deep sleep, ready to watch over them from the shadows until the next awakening.
