Lord Sunday (2010) (edit title/settings)

This final chapter in the "Keys to the Kingdom" series starts with Arthur falling, thousands of feet down from the Incomparable Gardens back into the Upper House. Arthur has wrenched the 6th Key from Superior Saturday and uses it to open the stairs. Because he was falling when he opened the stairs though Arthur plummets down the improbable stairs, unable to stop himself. Finally, by concentrating on one specific place he manages to pull himself off of the stair, returning at last to his home and Earth. Or so he thinks. Arthur finds himself on his bed and in his house. He's injured from falling down the staircase and his battle with Superior Saturday. Arthur uses the keys to heal himself, which also furthers his transition into a denizen. When he is healed, he goes down the staircase in his house and finds his mother, Emily, sitting on the sofa. Arthur tries to catch her eye and speak to her but she doesn't respond. Emily has never ignored Arthur. Then Arthur notices the other odd things going on, the windows in the house are all surrounded by huge hedges.

Meanwhile, Suzy has been taken captive by Superior Saturday and her minions. While she hangs in a human sized bird cage, thousands of feet in the air, Suzy makes a deal with a denizen Giac. Giac is a Sorcerous Supernumerary (meaning he failed his final sorcery exams). She persuades Giac to free her and accompany her to the Citadel in the Incomparable Gardens.

On Earth, Leaf, responsible for the Sleepers from Lady Friday, struggles to cope with the aftermath of a nuclear strike and desperately needs help. She walks to a designated place to get help from the Army and meets Arthur's oldest brother. She brings him back to Lady Friday's private hospital and becomes a target for intruders from the House, namely Lord Sunday's Dusk and his 'pet'. Within the House, Nothing continues to rise and must be stopped before it can destroy the entire House and Universe. Sunday intends to force Arthur to hand over the Keys and the Atlas to the House by controlling Leaf and his mother; to this end, he dispatches the "Reaper" (Sunday's Dusk) to take Leaf through the Front Door. The Front Door is filled with Nithlings and is, indeed, collapsing through contamination by Nothing. The Lieutenant-Keeper of the Door is vanquished in battle with them. Before he passes into Nothing he calls Sunday's Dusk to him and passes control of the Front Door to the only person available - Leaf. Leaf, being the new Lieutenant-Keeper, cannot be compelled to leave the Front Door, so the Reaper goes back to Lord Sunday to report his failure.

Back with Arthur a Piper's child employed as a gardener enters the house with a flaming pitchfork; Arthur grabs and deactivates it, and forces the boy to lead him out of the house. The boy professes not to have heard of the upheavals among the Trustees; he thinks Arthur is the Reaper (leading Arthur to suspect that the Reaper is Sunday’s Dawn, Noon or Dusk).

As they leave Arthur's house, they are ambushed by Sunday's Dawn and Noon; and the Piper's child reveals himself to be Lord Sunday in disguise. After chaining him up by his arms to a colossal dragonfly, the form of transport commonly used in the Gardens they fly him over the Gardens to a smaller replica of the clock face that the Old One is bound to. Arthur, his Keys overcome by the superior power of the Seventh Key, tries to escape by using his own innate powers to form something out of Nothing; he fails to create anything, but he brings his childhood toy, Elephant, to life. He sets it to search for his confiscated Keys; meanwhile, he calls the Mariner to come and rescue him. Hours later, the Keys are sent to him and Arthur is able to free himself. Though at a cost. Elephant has been killed.

Leaf has ventured to the Middle House via portal and has joined forces with Suzy's band of motley Raiders in an attempt to infiltrate the Upper House, in order to prepare elevators for the Army of the Architect to get through to the Gardens. Fred Initial Numbers Gold, during an attack by the Piper's army, accidentally picks up Leaf's sword, and with it the post of Lieutenant-Keeper of the Front Door.

Arthur battles with Lord Sunday, who also has to contend with an invasion by the combined forces of the Piper and the formerly Superior Saturday. The battle is taken to the Elysium, the epicenter of creation; it is here that the seventh part of the Will, a withered apple tree, is kept in a gilt cage. The Mariner opens it at Arthur's behest, but is killed in the process. The freed Will traps Sunday while Arthur claims the Seventh Key (in the form of a small key). When Dame Primus bites into an apple from the manifestation of Part Seven of the Will, the Will is made whole; Arthur unknowingly becomes its channel for its intended purpose - the destruction of the House. The Old One is freed, and He steps into the Will; it is explained that the Architect split Herself in two at the beginning of Creation to speed the evolutionary process, and the Old One is in fact a part of Her (but he had to be chained up when his views grew distinct from Hers), and the manifestation of the Will is the Architect in Her entirety. She reveals that, bored with life, She wished to return to Nothing, to see what it was like to die. She could not do so, however, without destroying the House, because in her anger She had chained the Old One to the fate of the House, and the Old One was anchoring her to existence. The Architect destroys the remnants of Creation with the powers of the Keys.

Arthur, now omnipotent, survives and is anointed "New Architect" by the fading thoughts of the Architect. This is why She needed a mortal Heir, to provide a creative spirit to renew the Universe. Arthur decides to remake the Universe exactly as it was, using the Complete Atlas of the House to provide the template. Because the Atlas holds a record of the House and Realms a few seconds before the destruction, Arthur is unable to save his mother, but he does split himself into the New Architect and the human Arthur, before his transformation into a denizen of the house. The new Arthur is not quite the same, being immune to all disease and with all the knowledge he acquired on his journey. He sends Arthur and Leaf back to Earth, by recreating the Seven Dials. It is also implied that the new Arthur is immortal.

In the new Creation of the Universe, Suzy reveals her desire to be the new Lady Sunday, and agrees with the New Architect to remake the House. The New Architect reveals he will soon bring back Doctor Scamandros, Fred, and Giac, the sorcerer, who could all help with the creation of new Denizens. The book ends with the new architect being called Art by his friends.