Wednesday being the third day of the week (if you don't start at Sunday of course), there are no prizes for guessing that this is book three of The Keys to the Kingdom series. If you haven't read Mister Monday and Grim Tuesday, please look no further - without the two preceding books you'll be up a creek without a paddle if you try this one on its own.
Arthur is still recuperating in hospital from his adventures in book two when he is summoned for lunch by Lady Wednesday, Trustee of the Architect and Duchess of the Border Sea. A ship is dispatched to pick him up, which is an unusual mode of transport seeing that he is in a hospital far away from any major body of water. Arrangements are made to resolve this minor inconvenience, and soon Arthur is adrift on his steel bed accompanied by his friend Leaf who was visiting at the time.
Unfortunately the crew of the Flying Mantis picks up the wrong passenger, and Arthur is left adrift, broken leg and all, and with sinking bed and spirits. His spirits are "buoyed" in the nick of time when he discovers a convenient flotation device, but this turns out to be a not a blessing in disguise, but a disaster in the making.
Caught red-handed fooling around with pirate treasure, he is picked up by the crew of a ship named the Moth, and barely escapes being captured by the dread pirate Feverfew (owner of said treasure) and his ship of bone, the Shiver. Soon it's time for lunch with Lady Wednesday, who is cursed with the sin of gluttony, and has been transformed into a creature worthy of her voracious appetite. Barely escaping being a part of the menu, Arthur agrees to an alliance for ownership of the third key and sets off on his third quest of the week in the name of the Will. This proves to be a huge pill to swallow, and gives him a sinking feeling in the pit of his stomach.
The most exciting adventure of the series so far, this one is heavily laden with sea-faring rats with both two and four legs, sorcery and heroic deeds, and the humor is at its very best. It will be very difficult for Garth Nix to top this one.