In this sixth book of Garth Nix's Keys to the Kingdom series, our main character Arthur must face a formidable being that rules the Secondary Realm (an other-worldly realm that runs parallel to the real world) and claim a magical key that brings him one step closer towards claiming his full right as the true heir and ruler of the Secondary Realm. Arthur is a normal kid who is forced to collect seven magical keys from the Secondary Realm as well as the seven parts of the Architect's Will. The Architect is the being who created the Secondary Realms and the one who named Arthur as the true heir. Once he has collected all these components, he can take full control of the Secondary Realms. There are many powerful beings who won't easily obey the Architect's will and allow Arthur to rule over them, however. Beings such as Mister Monday, Grim Tuesday, Drowned Wednesday, Sir Thursday, Lady Friday and, in this installment of the series, a being named Superior Saturday. Arthur has fought and retrieved five magical keys as well as five components of the Will so far - now he faces one of the oldest and most powerful beings of the Secondary Realm.
The story begins with Arthur receiving a phone call from his brother, who is in the Army. His brother tells him that the city is about to be nuked because the government believes the city is infected with a plague. The plague is a mind-controlling mold that Superior Saturday had devised to take over the Secondary Realm as well as Arthur's own world. Arthur and his friend Leaf panic upon receiving this phone call. Arthur is reluctant to use the magical keys he has collected from his previous adventures because the magic is slowly turning him into a being of the Secondary Realm. Once Arthur uses too much magic he will become immortal and will not be able to live in his own world anymore. At this moment in time, however, Arthur sees no other way to stop the nuke from destroying his city but to use his magical key. Arthur commands his key to keep his city in a protective bubble. After the magic does its work, Arthur realizes that his entire world and its citizens are now frozen in time, including Leaf. Arthur wears a ring that tells him the level of magic that has transformed him. The ring now says that he has become 60% a being of the Secondary Realm. Dejected, Arthur feels he now has nothing to lose and uses his magical key to travel back to the Secondary Realm.
In the Secondary Realm, he finds that the destructive substance called Nothing (a substance that is like anti-matter and turns all things into nothing-ness) is threatening to destroy great swathes of the Secondary Realm. Arthur uses the magic of his key to protect various domains in the Secondary Realm however even the magic of the key can only slow down the advance of Nothing. Arthur transports himself to his headquarters in the Secondary Realm where he commands Dame Primus to help him slow down the flow of Nothing. Dame Primus is a sentient being who is the amalgamation of all components of the Architect's Will that Arthur has retrieved so far. Arthur is beginning to suspect that Dame Primus is hiding something from him. In order to reduce her power a bit, he asks Dame Primus to split herself up into two less powerful beings in order to more efficiently travel to different parts of the Secondary Realm and contain the Nothing that is seeping in and destroying the world. Arthur is also feeling the effects of using too much of the key's magic - he's also at risk of letting the power of the keys get to his head.
Arthur and his friend, Suzy, travel to the seas of the Secondary Realm in order to recruit some ship rats to help him. He plans on retrieving the sixth magical key of seven magical keys from a being called Superior Saturday. The ship rats have an extensive network of spies all throughout the Secondary Realms and help Arthur and Suzy sneak into Superior Saturday's domain. They paint them with a magical paint that disguises them as rats so they can freely travel around Superior Saturday's domain without raising suspicion. Once Arthur makes it to the basement of Superior Saturday's domain, his magical disguise falls off and he joins the Chain Gang which is a gang of children that service the massive mechanical chain system that runs Superior Saturday's building. The chains in Superior Saturday's buildings are used to raise and lower office spaces up and down the many floors that make up Superior Saturday's sky-scraper building. The office spaces rise up when Superior Saturday promotes someone or are lowered when Superior Saturday demotes someone. The higher up the office is raised, the more sycophantic the office worker is. When a worker gets promoted, his co-workers are filled with jealous rage and refuse to remain friends. All the office workers are sorcerers and they can sense when magic is being used so Arthur and Suzy must be very careful and bide their time.
Arthur and Suzy fit in with the Chain Gang at first, but the leader of the Chain Gang, Alyse is suspicious of who they are. Later on, Arthur finds out that Alyse has been informed to be on a lookout for two children. Alyse betrays them by reporting to her superior that Arthur and Suzy are with her. Arthur finds out about the betrayal and forces Alyse to tell him how to access the water reservoir in Superior Saturday's building. Later on, he forgives Alyse and gains her allegiance and help. Alyse helps Arthur and Suzy travel the elevator up to the top-most floor where the opening to the water reservoir is found. Arthur starts hearing the voice of the sixth Will in his head and with its encouragement, it summons the Will. Suddenly, large steamships appear. The steamships are manned by the Piper, who is another powerful being that also claims to be the true heir to the Secondary Realms. All the magic that is being used alerts Superior Saturday, who showers the lower floors with fiery magic of her own. Arthur finds out that Superior Saturday has devised a machine to pierce through to a place called the Incomparable Gardens which is the epicenter of the Secondary Realms. Arthur spies Superior Saturday who is observing the whole process from her protected platform. The process of drilling through into the Incomparable Gardens is dangerous and Arthur uses more magic to protect himself. He thinks he's probably fully immortal now, but he doesn't care. Just as Superior Saturday finally notices him, Arthur claims the sixth magical key.
Best part of story, including ending:
I thought it was interesting that Arthur's personality is becoming colder and more impassive, indicative of the fact that he's becoming more god-like and immortal as he uses more of magic.
Best scene in story:
My favorite scene was when Arthur observes an office worker get demoted and a personal rain cloud just raining down upon the poor worker. I thought it was quite a funny and surreal scene.
Opinion about the main character:
I'm not sure I like that Arthur's changed from using his magic. He's losing more and more of his humanity - I hope he finds a way to dispel the magic in his system so he can be a normal kid again.