Every night all human dreams are played out in Nightopia and Nightmare, the two parts of the dream world. In Nightopia, distinct aspects of dreamers' personalities are represented by luminous colored spheres known as "Ideya". However, the evil ruler of Nightmare, Wizeman the Wicked, is stealing this dream energy from sleeping visitors to gather power to take control of Nightopia and eventually the real world. To achieve this, he creates numerous beings called "Nightmaren", including two acrobatic, jester-like, flight-capable beings called Nights and Reala. Nights, however, rebels against Wizeman's plans, and is punished by being imprisoned inside an Ideya palace, a gazebo-like container for dreamers' Ideya.
William Taylor and Helen Cartwright are the two chosen dreamers. Will is an aspiring soccer player, while Helen is a prodigy violinist. They're both from a London-based city known as Bellbridge.Both children are close to their respective parents; Helen her mother and Will his father. However, the closeness between them has changed over the years; Helen has chosen to spend more time with her friends than with her mother practicing the violin, a choice which has begun to fill her with guilt, while Will's father is transferred to another city for work and leaves his son by himself. Both children suffer individual nightmares and come under attack by the Nightmaren, who chase them into the world of Nightopia. There, the two children separately meet the wise Owl and the playful dream jester Nights, who has the ability to "dualize" with the children, allowing them to share Nights' body and fly through the skies. Learning that the wicked Wizeman is plotting to take over the dream world and then emerge into the real world, the children and Nights resolve to stop Wizeman, but face hindrance from the Nightmaren he commands, particularly Nights's former comrade Reala.
After defeating all the Nightmaren and finding the Ideya of purity, intelligence and growth, Helen go up the stairs with NiGHTS, NiGHTS sees the Ideya of hope while Will follows, but then there's and earthquake and Wizeman appears, leaving NiGHTS unconscious, he grabs NiGHTS along with the last Ideya and takes them into the dark sea of Nightmare, and captures Helen. Will jumps in to follow them. During a blackout, Helen panics due to her fear of darkness, and loses her red Ideya, beginning to plummet to the ground. Will saves her, restoring her Ideya, and together they fly to where NiGHTS is being held prisoner. After unlocking NiGHTS, Reala appears. NiGHTS challenges him to battle, which NiGHTS wins. Suddenly the last Ideya appears, but Wizeman too, revealing that defeating him will destroy all his creations- including NiGHTS. After the battle, the Yellow Ideya is returned to the two children, just before NiGHTS disappears with a graceful bow in a cloud of white light.
Will wakes up crying, thanking NiGHTS.
Will is then seen playing in a tied soccer match in the latter half. The ball comes to him, and he is blocked, with all teammates being blocked by other players. Reminiscing his time in Nightopia, he jumps up and scores the winning goal. He sees his father in the crowd, cheering him on, and begins laughing with his team.
Helen is seen running towards the town concert hall, where her mother is waiting. Inside, they flawlessly play their recital, and during the subsequent standing ovation Helen spots her friends in the crowd.
That night, Helen guides her mother to the outside concert theater, which is empty, and begins to play Dreams Dreams on the violin. Meanwhile, Will is walking down a street with his father and friends, kicking his ball. He hits the ball and it falls down some stairs, while Will runs after it. Stopping to pick it up, he hears Helen playing, and begins to follow the music. A blackout suddenly happens, and Helen screams, thinking Wizeman has returned, closing her eyes and curling into a ball. When the lights come back on and she opens her eyes, Will is standing there with his hand out. Helen reaches out to take it, and it begins to snow. The two laugh, and the screen fades out.
Late that night, while Will is asleep, the camera flies to the top of Bellbridge spire, where NiGHTS is seen playing his/her invisible flute, revealing that (s)he survived.
- Leonardo DiCaprio as the voice of NIGHTS
- Alex Ferris as William "Will" Taylor
- Chloë Grace Moretz as Helen Cartwright
- Gary Oldman as the voice of Wiseman
- Tom Cruise as the voice of Reala
- Michael Douglas as the voice of Owl
- TBA as Queen Bella