Drowned Wednesday

This is Book Three in Garth Nix's blockbuster fantasy-adventure series, "The Keys to the Kingdom," following the best-selling "Mister Monday" and "Grim Tuesday." Arthur Penhaligon has a broken leg and a bad attack of asthma, but there's no time for recovery. Drowned Wednesday has sent a ship to pluck him from the safety of his bed, miles from any ocean, and sail him back to the House.
From hospital room to the high seas, Arthur must battle pirates, storms, monsters made of Nothing and a vast beast that can't stop eating. Arthur struggles to unravel the mystery of the Architect's disappearance, and the plotting of the Trustees. For the sake of all that dwell in the Secondary realms, he must discover the third part of the Will and claim the Third Key.
But first... can Arthur trust the Raised Rats? Where are Leaf and Suzy? And how will he survive life aboard ship on the treacherous Border Sea?