Sir Thursday - Garth Nix

Out-of-this-world magical adventure series for teens from the award-winning, New York Times bestselling author of Sabriel and the Old Kingdom series.
Seven days. Seven keys. One very unlikely hero.IT'S THURSDAY. Following their adventure on the Border Sea, Arthur and Leaf are set on heading home. But only Leaf can make it through the Front Door. Arthur is blocked because someone - or something - has assumed his identity and is taking over his life. Before Arthur can take action, he is drafted by the strange Sir Thursday and forced to join the Glorious Army of the Architect. While Leaf tries to banish Arthur's double on earth, Arthur must survive his basic training, avoid getting posted to the front, and work out how he can free Part Four of the Will.Is this a war that Arthur can win... or is his only hope to escape it?