This book starts immediately after Lady Friday has been defeated. Arthur returns home with the surviving sleeps and finds out that General Prauvil (working under direct orders from Superior Saturday) has ordered mini nuclear weapons to be fired at East Area Hospital because of the wide array of diseases coming out of the area. Arthur, who is still holding the 5th key does a bit of sorcery and stops time on Earth. Everything is surrounded by a glowing red light and Arthur knows that his time stop is temporary. He decided to return to the House to get the 6th bit of the Will and try to stop Saturday and her minions from nuking his home town. Arthur uses the 5th key, bringing himself back to the Lower House. He finds the Lower House collapsing into itself as Nothing eats at it. Arthur temporarily is able to contain the Nothing, giving him time to join Dr. Scamandros in the Lower Coal Cellar. There he find Scamandros investigating the encroachment of flowers in the cellar. As the House grows weaker, the Old One is growing stronger and more fit. Arthur talks to the Old One, who tells him that his prison will soon fail. Arthur tells the One Old that he had planned to release him when he got mastery over the whole House and the Old One professes that he is grateful.
Arthur and Dr Scamandros escape to the Great Maze, where Dame Primus tells Arthur that Nothing is encroaching on all of their territory. Dame Primus insists that Arthur work with him to stop the Nothing and save what they can of the Border Sea, the Great Maze, and the Middle House. Arthur tells Dame Primus that the best defence is a good offence and he insists on journeying to the Upper House to find the Will and possibly stop Superior Saturday. Arthur also insists that Dame Primus split herself into two pieces to better stop the Nothing. She does this reluctantly and Arthur, Suzy, and Dr Scamandros journey to the Border Sea to talk to the Raised Rats.
The Raised Rats have a secret way into the Upper House and agree to help Arthur get there and give him reasonable help if they can once he is there. While Arthur is aboard the ship he kills one of the Piper's New Nithlings, who are being given a ride by the Rats to destination unknown to Arthur. Arthur has Scamandros transform him and Suzy into Raised Rats and them take a special simultaneous bottle to the Upper House. There they meet Dartbristle, a Raised Rat that has agreed to help them get in touch with the Pipers Children working in the Upper House. In the Upper House Piper's Children maintain the system of chains that allow for the moving of offices.
Allyse (sp?) is in charge of the group of Piper's Children that Arthur and Suzy are assigned too. In Upper House, Piper's Children are called Grease Monkeys. She gives Arthur and Suzy tasks on her team but she is suspicious of Arthur, who no longer really looks like a Piper's Child at all. At one point, Arthur asks her for directions to the nearest reservoir and she tells him to go find Dartbristle. Unbeknownst to Arthur, Allyse has a book that describes where everything is in the Upper House. Once Arthur finds this out, and knows he has been betrayed, he finds Allyse and forces her to help him. She agrees, because she really has no choice, and directs Arthur to the nearest reservoir.
Arthur needs to find the nearest reservoir because it has been raining in the Upper House for 10,000 years - the exact amount of time that Superior Saturday has been a Trustee. Arthur discovers that the Will has been separated into drops of rain. He finds the reservoir and calls the Will back into a corporal shape, a raven. Arthur is discovered by Superior Saturdays sorcerers and is separated from Suzy. Arthur gets flushed down an enormous drain and Suzy is taken captive.
Once Arthur emerges from the drain, he finds Dartwhistle throwing a simultaneous bottle into the water. These bottles allow for the New Nithlings travelling with the Raised Rats to enter the Upper House with The Piper. The Piper begins to attack Saturday and her forces. Arthur runs out and joins a group of Denizens. Superior Saturday has finally managed to reach the top of the Upper House and is preparing to attack Lord Sunday. Arthur rides up with one of the conveyances and emerges in the Incomparable Gardens. There, he finds Superior Saturday and her highest ranking sorcerers battling enormous insects that help to guard to garden. Arthur, seizing his opportunity, calls for the key. Saturday battles him back, managing to knock him down the hole she had created to breach the Gardens. As Arthur falls, he holds both the 5th and the 6th Keys. This part of the series ends with a cliffhanger, with Arthur falling 14,000 feet, Suzy being held prisoner, Arthur's mother still missing, Arthur's home about to be attacked with mini nuclear weapons, and the Piper attacking the Upper House.