This book follows Elmer Elevator and his friend Boris, a baby dragon, as they attempt to rescue Boris's family from men who have trapped them in a cave in the remote mountains of Blueland.
The story opens with Boris flying northward from Nevergreen City toward Blueland, a hidden land surrounded by Awful Desert. He is eager to reunite with his six sisters, seven brothers, and parents, but his large size, blue-and-yellow stripes, and gold-colored wings make him easy to spot. At dawn, he finds a culvert, a tunnel carrying a brook under a road, large enough to crawl inside. He wades into the shallow water and falls asleep.
Someone has seen him. Mr. Wagonwheel, a farmer in a nearby yellow farmhouse, catches a glimpse of something blue, yellow, and gold galloping past and declares the creature a "Blue Demon." He sets out to hunt it, but rain has washed away Boris's footprints. Meanwhile, the farm cows have discovered Boris in the culvert. After hearing he is a baby dragon on his way home, the sympathetic cows decide to protect him. When Mr. Wagonwheel approaches, they huddle around the culvert opening as if drinking water. The farmer assumes no monster could be nearby and moves on. The cows guard Boris all day, and he flies away safely after dark.
Boris flies north through the night, turning westward across Spiky Mountain Range toward Awful Desert. He realizes with alarm that the desert is unusually clear, with none of the sandstorms that normally make the region impassable. In such conditions, men could cross into Blueland and discover his family. His fears are confirmed when he spots a campfire on the mountain slope and eavesdrops on a group of men. They report trapping 15 dragons in a cave with only one apparent entrance. Boris is horrified: The 15 are his entire family. The men discuss selling the dragons to zoos.
Boris knows something the men do not. The cave has a second entrance: a small tunnel that only he and his two youngest sisters had once been small enough to use. He crosses between two peaks, descends into Blueland's green alpine meadows, and sees the men guarding the cave across a lake with an enormous net. He clears the hidden tunnel entrance and squeezes inside but gets stuck partway through. His sister Eustacia hears his cries, and his mother recognizes his voice. Boris warns them to stay away from the main entrance and says he has a friend who may help. After backing out, he overhears the men planning to search for other entrances. Afraid they will find the tunnel, Boris re-covers the entrance and flies to Nevergreen City for help.
Boris rests during the day at a brook in Spiky Mountain Range, then continues south at dusk. Over the coast of Popsicornia, a ship's searchlight finds him. He zigzags to escape the beam and eventually arrives at Nevergreen City at dawn, gliding unseen into Evergreen Park.
The old alley cat, who originally told Elmer about Boris, spots the dragon landing in the park and wakes Elmer early Saturday morning. Elmer finds Boris hiding in the cab of a steam shovel at a construction site. Boris explains his family's plight, and Elmer agrees at once to help. The three friends spend the morning devising a rescue plan. That afternoon, Elmer empties his savings to buy 16 whistles, 16 horns, a cap pistol with caps, heavy string, chocolate bars, and Fig Newtons. He also packs his jackknife and a flashlight in his father's knapsack. After supper, he sneaks out. The old alley cat says goodbye, explaining she is too old for the journey but will look after Elmer's parents. Elmer climbs onto Boris's back, and they fly north.
During the flight, Boris describes his family: his blue father, yellow mother, six green sisters, and seven brothers, each with a unique pattern of blue and yellow. He tells Elmer about their peaceful life in Blueland, where they tend meadows in summer and slide on the frozen lake in winter. Boris explains that dragons are gentle creatures who fled to Blueland to escape the knights who once hunted them nearly to extinction.
Over the coast, the ship's searchlight finds them again. The men on the ship spot both the dragon and a boy on its back. Boris dodges the beam and escapes when the moon goes behind clouds. They reach Spiky Mountain Range at dawn and rest in a forest. Meanwhile, Mr. Wagonwheel, traveling to the Seaweed City police to report his earlier sighting, sees the dragon with a rider overhead, but no one else witnesses it.
Elmer and Boris wait until late afternoon, then fly across the desert to Blueland. From the gap between the peaks, they see the men still guarding the cave, confirming the rescue is still possible. At the tunnel entrance, Elmer ties a whistle and horn on strings around Boris's neck and enters the tunnel, leaving Boris outside.
In total darkness, Elmer meets the dragon family and identifies himself as Boris's friend. He divides his last three chocolate bars among the 15 starving dragons and ties string necklaces with whistles and horns around each dragon's neck. He tries to examine the net at the cave entrance but cannot get close because the men are sitting nearby. He returns through the tunnel and gives Boris his final instructions: After hearing the cap pistol fire three times, Boris must blow his instruments as loudly as possible.
Elmer re-enters the tunnel and positions himself near the net inside the cave. He fires the cap pistol once and yells in a gruff voice, pretending to be a trapped man and calling out for "Frank" and "Albert." The startled men begin rolling away the boulders pinning down the net. He fires a second time, crying that the dragons have gotten him. The men frantically pull the net aside. On the third shot, Elmer runs back into the cave. Boris hears the signal and begins blowing his instruments while running across the meadow. Inside, all 15 dragons blast their whistles and horns. The noise roars through the cave and echoes around the mountains. Some men bolt at the sound of Boris outside; the rest flee in terror. Elmer shouts "Boris!" and races through the tunnel while the 15 dragons pour out of the cave, trampling the campfire. They zoom into the sky, still blowing their instruments, leaving the men scattered across the meadows.
Boris and Elmer fly away before the echoes die. Over the desert, the wind grows stronger and Boris smells sand, a sign that sandstorms are returning. The storms will force the men to leave Blueland, meaning the dragons may never be disturbed again. At midnight, Boris drops Elmer atop the Seaweed City Monument. Elmer asks Boris to tell his family their secret is safe. Boris hugs him and flies home. Elmer walks to the railroad station and buys a ticket to Nevergreen City. He sleeps through the train ride and arrives home at noon, where his mother feeds him a large meal.
The next morning, the story breaks in the
Nevergreen City News. Elmer's father, Mr. Elevator, reads aloud a report about 15 dragons escaping from Blueland, citing evidence from the ship's crew, Mr. Wagonwheel's sightings, and other witnesses. Mr. Elevator stares at Elmer and asks if he had anything to do with it. Elmer deflects, asking his father if he really believes "all that nonsense."