Sixth-grader Cole Randolph is excited to celebrate Halloween. His best friend Dalton convinces him that he’s not too old to trick-or-treat, and when he works up enough courage to ask his crush, Jenna, to meet him at the new haunted house in town, it looks like Cole’s going to have the best Halloween ever.
But the basement of the haunted house seems a little too realistic, and it soon becomes clear that the haunted house is a front for men who are kidnapping kids to work as slaves. Cole manages to hide as the slavers lead dozens of children, including Dalton and Jenna, down a manhole. Cole decides to follow them, but when he jumps down the manhole, he falls into another world.
He finds himself in a barren prairie, and a hooded figure tells him that he has arrived in the Outskirts, a place between worlds. The hooded man is a Wayminder, who can open the portal to the Outskirts. The Wayminder says that the slaves and freeborn in the Outskirts have marks that designate their status.
Cole realizes he could be enslaved if he doesn’t get a freemark. Cole follows the slavers’ wagon train and attempts to rescue his friends. But the slavers catch him, and they carve a magical bondmark onto the top of his wrist.
The wagon train is traveling toward the slave market at Five Roads. Some of the children, including Jenna and Dalton, will be sent to the High King of the Five Kingdoms because they have shaping potential, although no one knows what that term means. Cole is said to have zero shaping potential and therefore is of zero value to the king. The slavers sell him to a man who works for the Sky Raiders.
The Sky Raiders live on the Brink, a cliff overlooking an area that has no bottom. There is an eastern cloudwall at one border of the Brink called Eastern Cloudwall, and one in the west called the Western Cloudwall. The Sky Raiders make their living salvaging mysterious abandoned castles that float from the Western Cloudwall to the east.
Cole’s owner, Adam, lives in a large building called Skyport, built right near the edge of the Brink. Cole learns that his life as a slave for the Sky Raiders will be relatively pleasant. He won’t be treated too harshly and after 50 scouting missions, he’ll be upgraded to a much better job.
On the downside, he’ll have to risk his life daily as a scout for their salvage missions. He learns that scouts enter the floating castles first and look around to see if there’s anything dangerous. Most of the castles are occupied by semblances, which are magic apparitions that can look like people or monsters.
The semblances are not completely real and, although they can do damage while they’re in the air, fade away if brought to solid ground. A slave girl named Mira works as a shaper for the Sky Raiders and offers Cole pointers on how to survive his first few assignments. He receives one special shaped item, a Jumping Sword that will yank him away from danger if he points it in the opposite direction and yells “away.”
The next morning, Cole rides the skyship Domingo from Skyport until he’s close to one of the floating castles. From there, he boards a flying lifeboat and is lowered down to the castle grounds on a rope. The castle in question is full of semblances of working women, solemn-faced apparitions who walk about busily.
One of the women puts a shawl around Cole’s head and tries to hide him from a giant scorpion/centipede creature. Cole narrowly escapes the monster by using his Jumping Sword to evade its attacks and return to the lifeboat. All the Sky Raiders and scouts are impressed with his daring escape, though they’re disappointed that he didn’t salvage any treasures and only escaped with an old shawl.
On his fifth scouting mission, Cole talks to a semblance of a soldier, Lyrus, on one of the castles’ grounds. Cole makes Lyrus aware of the fact that he is living on a floating castle, which appeared out of nowhere and will soon disappear again. Lyrus has an existential crisis when he realizes that he has no future or past.
Lyrus says that in order to retrieve treasures from his castle, Parona, Cole must pass a test of bravery. Lyrus tells Cole to put the shawl on him, because the shawl makes semblances obey whoever puts it on them. Lyrus offers to take the test for Cole because he wants to prove his own worth as a hero.
After defeating a lion in combat, Lyrus grants the crew of the Domingo full access to the treasures of Parona castle. However, Lyrus becomes hungry for more glory and unleashes four other monsters so he can fight them, just as Cole’s Sky Raider colleagues board the castle, including Cole’s friend Mira and her shaper mentor, Durny. In order to save Mira and Durny from a cyclops attack, Cole uses his Jumping Sword to launch himself toward the cyclops’s eye, stabbing and killing it.
Unfortunately, when all the monsters are slain, Cole, Mira and a severely injured Durny are left on Parona without a possibility of rescue. Durny says they must construct a skycraft of their own. Knowing that he will die of his injuries soon, Durny says that Cole must protect Mira because she is an extraordinarily valuable person. Durny himself was Mira’s protector, but he now passes that duty on to Cole. After Durny dies, the two children escape Parona in a flying coffin and return safely to Skyport.
At Skyport, Mira tells Cole that there are five kingdoms in the Outskirts: Sambria, Necronum, Elloweer, Zeropolis and Creon, with Junction City lying at the midpoint between all five. A different Grand Shaper once ruled each kingdom, but 60 years prior, a man called the High Shaper took control of all five kingdoms. The High Shaper grew increasingly paranoid of possible threats to his power.
He ended up banishing most of the Grand Shapers and orchestrating a carriage accident so that all five of his magically talented daughters would die, eliminating the chance that they would rebel against him. Mira says that her mother lives in the High Shaper’s palace and has sent her a signal to warn her that danger is coming. She needs to escape from Skyport and requires Cole’s help.
The next day, legionnaires from the High Shaper arrive to take Mira from the Sky Raiders, but with help from Cole, she manages to escape. Mira, Cole, and two young slaves named Jace and Twitch fly away in a lifeboat but are pursued by the legionnaires. With no other option, the kids choose to sail into a cloudwall, even though they know that skycraft never return after entering a cloudwall. Inside the cloudwall, their lifeboat goes down a giant air funnel similar to a tornado, and they are caught in the safety nets of flying machines before they can fall to their death.
The flying machines deliver the children to a hidden castle called Cloudvale, home to Declan, the Grand Shaper of Sambria, who is in hiding from the High Shaper. Declan tells Cole, Jace and Twitch that the High Shaper’s five daughters didn’t die in that carriage accident after all — the High Shaper faked his daughters’ deaths so he could keep them imprisoned and use their shaping powers for his own purposes.
The queen helped her daughters escape, but none of the girls aged once their shaping powers were removed. Mira is really Miracle, one of the five princesses, and her powers are slowly returning to her. No one knows how the High Shaper stole his daughters’ powers. Declan says that most of Mira’s power has escaped from the High Shaper and has formed a semblance called Carnag, a monster that is terrorizing the citizens of Sambria.
Mira decides to leave Cloudvale to confront Carnag and try to reabsorb her powers. The three boys go with her, and Declan replaces their bondmarks with freemarks and gives them magical objects to aid them on their quest. Cole asks Declan how he can help his enslaved friends Jenna and Dalton, and Declan replies that by supporting Mira and helping her regain her powers, Cole could help start a chain reaction that would bring down the High Shaper, who made it legal to steal people from Earth as slaves in the first place.
The four kids travel through the dangerous Quiet Wood, where they have to maintain silence no matter what, and enter Brady’s Wilderness, a magical place full of milk-and-cookie ponds, hills of chocolate cake and other giant sweets. The sweetness of Brady’s Wilderness turns sour when an army of skeleton warriors and giant plastic dinosaurs attack them.
With the help of their magical items and a semblance named Amanda, they escape to the community of Middlebranch. At Middlebranch, they seek advice from Gerta, a friend of Declan’s who knows about Carnag. She points them in the direction of a nearby town, which was decimated by the monster.
When they finally encounter Carnag, the semblance is as tall as a tree and is made up of pieces of plants, rocks and broken objects. Carnag’s body contains several large cages, which are filled with living humans. Carnag catches Cole, Twitch and Jace and puts them in one of the cages.
Mira confronts the monster and tells it that it belongs to her, but the monster doesn’t want to be reabsorbed. It captures Mira and puts her in a cage, too. Cole hears the sound of a woman speaking from within Carnag, and he and the other boys follow a tunnel in the back of their cage and discover a middle-aged woman named Quima piloting Carnag. Quima wants to permanently separate Carnag from Mira, and Carnag believes that Quima has her best interest at heart.
Just as Carnag is about to kill Jace, Cole wraps his magic shawl around part of Carnag and commands her to lie down and release the people who are her captives. Mira uses magic to tear apart what’s left of the Carnag semblance and take back her own shaping energy. Quima doesn’t want to reveal any of the High Shaper’s secrets, but she mentions that she works in shapecraft, a kind of shaping that influences shaping itself, and that helping the High Shaper steal the five princesses’ powers was just part of a much larger plot.
After the Carnag incident is finished, a messenger named Joe MacFarland arrives to tell Mira that she needs to go to Elloweer to help her sister Honor, who is in distress. Cole learns that the High Shaper has been sending his new slaves all over the Outskirts to receive training, so there’s no telling where Jenna and Dalton are. Until he has a clearer path to finding his friends, he decides to stick with Mira and continue to aid her.