Drowned Wednesday

Drowned Wednesday is the third novel in the Keys to the Kingdom series by Garth Nix, in which Arthur Penhaligon must retrieve the Third Key and the third section of the Will of the Architect to claim mastery of the Border Sea of the House.

Plot Teaser
" On the third day, there were pirates.

Wednesday  has rolled around, and Arthur Penhaligon has an invitation to return to the House that he can't refuse. Drowned Wednesday has sent a ship to pick him up from the hospital...even though his hometown is miles away from any ocean.

From hospital room to the high seas, Arthur finds himself on an adventure that will pit him against pirates, storms, explosions of Nothing-laced gunpowder, and a vast beast that eats everything it encounters. Through it all, he is drawn deeper into the central mystery of the House. Arthur must find the third part of the Will and claim the Third Key - not just for himself, but for the millions (if not trillions) who will suffer if he doesn't.

The first step? Surviving life aboard a ship on the Border Sea... "

(source: Goodreads)

Plot Synopsis
This section contains spoilers about the content and ending of the novel.  Arthur Penhaligon, in the hospital for the broken leg he was left with at the end of Grim Tuesday, is visited by his school friend Leaf. As he is explaining to her the House and his invitation from Lady Wednesday, the hospital floods and the two are set adrift on his hospital bed on the Border Sea of the House. They are set upon by a ship called the Flying Mantis, and while Leaf is brought aboard, Arthur is left on his bed. He seeks shelter on a floating buoy that stains his hand red, and is eventually rescued by the crew of the Moth and brought aboard by the second mate, Sunscorch. In exchange for the treasure under the buoy he discovered, they agree to take him on as a passenger. Unfortunately, the treasure was placed under the buoy by the pirate Feverfew, who comes after the Moth to reclaim his treasure. After fleeing to a Secondary Realm through a portal produced by the sorcerer Dr. Scamandros, the ship is beached. Sunscorch takes over ship repairs, while Captain Catapillow and his valet Ichabod, not seamen by nature, outfit Arthur according to his role as Rightful Heir. Scamandros gives Arthur a tool to check on Leaf and helps Arthur send a message, but then sends another message of his own. Arthur uses the enchanted mirror to discover that Leaf is being held prisoner. Wednesday's Dawn arrives shortly thereafter to take Arthur to the promised luncheon with Lady Wednesday, who has unfortunately been turned into an enormous, gluttonous leviathan. She assumes her human form to meet with Arthur, but eats constantly and maintains human form only long enough to tell him she will give him the key freely if he helps her regain her original form. Arthur agrees and requests that he be delivered to Leaf's last known location.

At the Triangle, Arthur meets a crew of Raised Rats who tell him that Leaf has been pressed as a ship's boy aboard the Flying Mantis and agree to help him in exchange for information about the Will. Arthur sends a message to Dame Primus, requesting fuel for a submersible and the aid of Suzy Blue. Meanwhile, Arthur unwittingly pulls Dr. Scamandros through an enchanted watch and is informed that the rest of the Moth 's crew has been captured by Feverfew. Dame Primus sends fuel and Suzy, and the Rats -- led by Captain Longtayle -- set out for Feverfew's secret hideout, a worldlet hidden inside the whale Wednesday's stomach. Once in the stomach, Arthur and Suzy leave the rest of the crew aboard the submersible and enter the worldlet disguised as rats. In a jungle, they discover the Followers of the Carp. The Carp turns out to be the third part of the Will, and it accompanies Arthur and Suzy -- along with four of the Followers -- back towards the worldlet exit. Unfortunately, they stumble across Feverfew, who agrees to exchange blows with Arthur. Arthur is able to prevail, but not before Feverfew sets the worldlet to collapsing.

The submersible has vanished, so Arthur and the Carp, now accompanied by Leaf and the rest of the enslaved crews, find a passage from the captured Moth to the submerged Port Wednesday. Once back in the Port, the Will commands Lady Wednesday to appear in her human form. When she transforms, she gives Arthur the Third Key and he uses it to free her from her ever-hungry prison. Due to the Nothing she consumed as a whale, she dies, but thanks Arthur for the dignity of a free death. Arthur vows to return briefly to his own world and then return to deal with Sir Thursday. An epilogue reveals that Arthur's place in the hospital, the flooding of which has been explained away, has been taken by the Skinless Boy.

Sequels
Drowned Wednesday is followed immediately by Sir Thursday. It is a direct sequel to Grim Tuesday.