Nemo, Gabriel Damon experiences a vivid nightmare in which a relentless locomotive seems to chase him through darkness, a vision that foreshadows an extraordinary journey. The following day, he heads to a parade for a traveling circus with his loyal flying squirrel, Icarus, only to learn his parents are too busy to take him to the event. The night brings a cheeky attempt at sleepwalking for a sugar-delivery heist, which backfires when his worried mother catches him and sends him back to his room with a quiet but firm reminder to keep his promises.
That same night, figures from the circus appear in Nemo’s dreams, led by a whimsical organist who introduces himself as Professor Genius. They reveal they’ve been sent by King Morpheus of Slumberland on a mission: Nemo is to become the playmate for the princess, Camille. Although Nemo is initially hesitant about meeting a girl, a sweet gift of cookies from Camille convinces him to accept the invitation. The two embark on a fantastical journey to Slumberland aboard a dirigible, a vessel Nemo is allowed to pilot, which naturally stirs up a fair amount of comic chaos as he learns the ropes of royalty in a realm filled with wonder and peril. René Auberjonois as Professor Genius and Bernard Erhard as King Morpheus accompany this odd mission, and Morpheus places a golden key in Nemo’s care—one that can unlock every door in Slumberland—while warning him about a forbidden door bearing a dragon insignia. With Camille’s invitation still in mind, Nemo and Icarus roam the magical expanse hand in hand, absorbing the strange rules of a land where dreams take form.
Soon Nemo meets Flip, a mischievous clown who drags him away from prince lessons and into a series of escapades that ruffle the guards’ feathers. Tension climbs when Nemo’s actions land them in a hiding spot inside a cave, where the pair stumble upon a door Morpheus warned them never to open. Flip tempts Nemo to unlock it, releasing “the Nightmare” into Slumberland. The danger escalates just as Nemo is being crowned—he receives the royal scepter, the sole power capable of stopping the Nightmare King if he ever returns. The celebration is interrupted when the Nightmare breaches the castle, seizing Morpheus during a dance and leaving the court to search for a scapegoat, with Nemo blamed for possessing the key.
Nemo wakes in a sea-flooded room where seawater spills in and ejects him and Icarus into the ocean’s embrace. Professor Genius reassures Nemo that he should not shoulder the blame, and that Flip’s actions—particularly his deception about a map to Nightmare Land—are the true source of trouble. Fueled by a renewed resolve, Nemo vows to rescue Morpheus and set things right. The trio—Nemo, Camille, and Genius—return to Slumberland and rescue Flip from a perilous cannon ride aimed toward outer space, a consequence of Flip’s hidden knowledge about Nightmare Land’s map.
With the gang together again, they embark on a perilous voyage aboard a tugboat toward Nightmare Land. They’re soon swallowed by a colossal whirlpool and drawn into the goblin-haunted realm, where a band of shape-shifting creatures called the Boomps—Ooloo and friends—offer help in the quest to free Morpheus. A swarm of enormous bats from the Nightmare King’s army harasses them, and Nemo tries to wield the scepter, but the incantation isn’t fully recovered, causing another jolt of wakeful chaos back in Nemo’s bedroom alongside Icarus. The dream-world adventure falters, yet the Boomps return with renewed hope when Oompo delivers a letter from Morpheus containing the complete scepter incantation, guiding them to Nightmare Castle through a doorway in the sky.
Inside the fortress, the Nightmare King holds Morpheus and others hostage, demanding Norman-like obedience and the scepter’s possession. A fierce confrontation follows, culminating in Nemo’s use of the scepter to shatter the Nightmare King and restore light to Nightmare Land—though it seems Nemo has sacrificed his own life in the effort. In a dramatic turn, Morpheus revives him with the power of the scepter, acknowledging Nemo’s courage and forgiving the past. The kingdom rejoices as Morpheus embraces Nemo’s growth and blesses his ascent as prince. Camille escorts Nemo and Icarus home on the dirigible, and the two share a tender kiss, sealing a newfound bond between dream and reality.
Back in Nemo’s room, a remorseful talk with his mother leads to a heartfelt apology for breaking his promise and attempting to steal pie. In a warm family moment, his parents agree to take him to the circus the next day, fulfilling the promise he had made. Nemo gazes out the window with Icarus, hopeful for a brighter morning, knowing that Slumberland’s adventures taught him what it means to be brave, loyal, and true.
