The week is close to its end, and for Arthur Penhaligon, it can't happen soon enough. 
 At least, that's how it seems in "Lady Friday," the next-to-penultimate book of the Keys To The Kingdom series. Garth Nix's latest suffers from a bit of middle-book syndrome, but he keeps things interesting with a brewing three-way battle, a New Nithling ally, and a vampiric Trustee who sucks the experiences from her victims. 
 Arthur is struggling with a bunch of new problems, when he is given Lady Friday's resignation... and a transfer plate. The next thing, he's been transported to Lady Friday's frozen, mountainous realm. And unknown to him, Leaf has followed thousands of senior citizens (including her disabled aunt) into Friday's realm. 
 Arthur's dire situation becomes even more difficult when he learns that his friends Suzy and Fred have been forcibly drafted into the Piper's army (they're only allowed out with a New Nithling accompanying them). And Superior Saturday is claiming control over Friday's realm. Time is growing short for Arthur to find the fifth piece of the Will... but that can't stop Saturday and the Piper. 
 "Lady Friday" suffers from the "middle book" syndrome -- it's building up to the battle between Saturday, Arthur and the Piper, but not quite there yet. By the cliffhanger ending, Nix has spun up the beginnings of an epic conflict, which only promises to get nastier when Superior Saturday finally makes an appearance. And who knows what's going to arrive with Lord Sunday? 
 The plot is slower-moving and darker than the previous books, with lots of ruthless Denizens who want Arthur stopped, not to mention the haughty, cruel Friday stealing the good experiences from elderly mortals. And a measure of uncertainty has come into the plot, with the New Nithlings and their ambiguous loyalties. Even Dame Primus (four-sevenths of the Will) is getting unreliable. 
 But Nix includes the occasional quirky moment to lighten all this dark stuff, such as the rather funny Beast, and the fact that the New Nithlings just want to garden. It's a bit like Lewis Carroll writing a steampunk epic. And by the last few chapters, things speed up to breakneck pace, and even dealing with the latest Trustee won't fix things. 
 Arthur is under plenty of stress in this one, since every time he uses a Key, he comes closer to becoming a Denizen. So he has to rely mainly on his wits in this one, to deal with everything from savage Nithlings to Friday herself. And poor Leaf is even worse off -- she's far away from Arthur, and surrounded by some very nasty Denizens. 
 "Lady Friday" is the buildup to the grand finale of Garth Nix's newest series, and while it's slower than the other books, it holds the promise of a great "Superior Saturday."