The title could be referring to either the camouflaged RainWing village or the secret NightWing Kingdom, both of which are main 'hidden' locations in the book.
"Deep in the rainforest, danger awaits...
The dragonets of destiny aren't sure what to expect in the RainWing Kingdom - Glory hopes to learn more about her family, and since the RainWings aren't fighting in the war, all five dragonets think they might be able to hide safely for a while. But something deadly is stalking the peaceful kingdom, and the dragonets soon discover that RainWings have been mysteriously disappearing from the forest. When the RainWing queen won't do anything to find her missing tribe members, Glory and her friends set off on their own rescue mission - which leads them right back into enemy territory...."
The prologue starts with the False Dragonets of Destiny, which were mentioned in The Lost Heir's epilogue. They are as follows: Squid the SeaWing, Flame the SkyWing, Fatespeaker the NightWing, Ochre the Mudwing, and Viper the SandWing. Nautilus and Morrowseer converse, and Morrowseer decides to take train them personally, disapproving of what the Talons have done so far.
Part One: Rainforest Monsters
The dragonets and Webs are traveling through the borders of the Rainforest Kingdom. Before they've left the Mud Kingdom, they come across two murdered MudWings. When they progress into the rainforest, Starflight notices that Sunny is missing. One by one each dragon goes missing until Starflight hides and Glory dodges something. She orders the mystery dragons to come out. The shooters turns out to be RainWings. Glory meets two, Liana and Jambu. They offer to take them to the village. While her friends are unconscious from the darts, Glory takes her first sun time nap in the rainforest. When she wakes, she finds a sloth lying on her back, which she eventually names Silver. Jambu then shows her the village and they learn that they are related. They return to find their friends awaking and they go to meet Queen Magnificent. While waiting in line, she meets Mangrove, a grumpy RainWing, who mentions that his partner Orchid is missing as well as at least twelve other RainWings, and Bromeliad, a venom trainer, who mentions that a dragonet named Kinkajou has also gone missing. Glory suggests that they go to the queen together, since they're both there about missing dragons. When Mangrove, Bromeliad, and Glory see Queen Magnificent, Glory suggests someone investigates, and Mangrove says Glory should find the missing RainWings, and Queen Magnificent agrees. When Mangrove and Bromeliad leave, Tsunami, Starflight, Clay, Webs, and Sunny come in, and ask Webs for help. Maggie was relucant and carless about Web's health, seeming to not care much. After some prompting from Sunny, the queen directed them to the RainWing healers. After they leave the queen's treehouse, Tsunami, Webs, and Sunny head off to the healer's hut, and Starflight and Clay join Glory as she sets out to find the missing RainWings. They speak to Mangrove, and he leads them to a giant fallen tree. Glory picks up a horrible stink, and asks Starflight if he can identify it, since he seemed to have a stronger sense of smell. They find a dying sloth by a stream, which Clay puts out of its misery. Glory looks around and discovers an animus-made tunnel to the Sand Kingdom in a boulder. Starflight and Mangrove return to the village, while Glory and Clay stay to watch the tunnel overnight. While they watch, something comes by, eats the sloth, and disappears. In the morning, Sunny, Tsunami, Starflight, and Jambu arrive, and they discuss what to do about the tunnel. They settle on Glory and Clay going in with vines. When they go through, they find themselves in the Kingdom of Sand, within sight of Princess Burn's Stronghold.
Part Two: Sand, Ice, and Smoke
Glory and Clay take a look around from the mouth of the tunnel's end in the Sand Kingdom, and return to the rainforest. The dragonets and Jambu talk over the missing RainWings and the tunnel. Then Mangrove suddenly dashes out of the trees and into the tunnel, and flies off to the Ice Kingdom to try to find Orchid.
After flying for the rest of the day, they settle down for the night in rocky terrain. In the morning, Glory flies ahead, sights Princess Blaze's Fortress, and sees a NightWing assassin named Deathbringer settling down. Using an IceWing disguise based on Fjord, she questions him on what he is doing. She secretly has a crush when meeting him.
Then Glory and Jambu, disguised as IceWings, go meet Blaze who is staying at the Ice Kingdom. Deathbringer then attempts to kill Blaze after she is brought to the Dragonets. Blaze's neck gets cut by one of the two "sharp silvery discs" and Tsunami's wing, after shielding Blaze, also gets cut. Glory attacks Deathbringer when they hear the IceWings coming and takes his weapons, using one to cut him somewhat. This makes Deathbringer surrender. In fear of getting imprisoned again, the Dragonets leave, with Blaze's neck healed. Later, when they returned, Glory is kidnapped by the NightWings. She escapes with the help of Clay, Deathbringer, and another captured RainWing named Kinkajou. When she gets back, she tells Magnificent about what happened. Seeing that the NightWings have them, she refuses to save them. Glory challenges Magnificent to the throne.
Part Three: A Throne in the Treetops
The RainWings have a system of picking a queen without killing, where there are competitions for the throne. Magnificent and Glory each assembled their teams. Jambu and Exquisite competed in the tree gliding and Exquisite likely cheated, nearly killing Jambu. Tamarin, a blind RainWing, and Fruit Bat competed in the flower finding hunt. Tamarin won. Glory and Magnificent competed in a camouflage contest, and Glory lost. Mangrove and Dazzling competed in a fruit scavenger hunt and even though Dazzling cheated, Mangrove won. The last contest was between Queen Grandeur and Kinkajou in venom shooting. When Kinkajou protected a sloth from Grandeur's venom, venom hit Kinkajou. Glory does the venom test and is related to Grandeur, so she successfully saves Kinkajou. Grandeur, who was the original queen, forfeits and Glory becomes the Queen of the RainWings. Clay crashes in and tells her that Starflight had left and may have warned the NightWings that the RainWings would attack.
Fatespeaker and the false dragonets are upset in the Night Kingdom. There is no food, it is dark and smelly, and every one of her friends are fighting. Fatespeaker spots some NightWings carrying an unconscious dragonet to the fortress. It is actually Starflight, but she doesn't know who he is yet, although she has a feeling he is important.
- The note from the author says, "For Elliot, born in a wonderful Year of the Dragon, like these books."
- The Hidden Kingdom has been voted 4.56 stars on Goodreads
- The main protagonist is Glory.
- This book has the same number of chapters as The Dragonet Prophecy, at 35, having the most number among the other books.
- The Hidden Kingdom and The Lost Heir have the same number of pages, at 296.