Grim Tuesday by Garth Nix

Pages: 321
Rating: 7/10
Main Conflict: Arthur Penhaligon doesn't think he'll need to return to the strange house he nearly died in, in which resided the 7 days of the week. One of which, Mister Monday he defeated and stole one of the Keys to the Kingdom, a weapon which enables possesion of one of the days of the week. But the new day brings new enemies. Grim Tuesday, the supplier in material goods to the other days of the week, is requesting payment for all the items he crafted for the old Mister Monday, from Arthur, the new Monday and everybody in his world. He must defeat Grim Tuesday and win his Key to save Earth from Grim Tuesday's servants.
Best Part: To find the second part of the Will, which tells that the Keys are to go to the rightful heir, Arthur, he and his friend Suzy Blue, must ride a sunship to the center of the sun. After fighting through a legion of vicious sunsprites, they find the second part of the Will, the power of which they use to retrieve the second Key to the Kingdom from Grim Tuesday.