The Diamond of Darkhold (Books of Ember Series #4)
Well, after an utterly pointless, irrelevant book 3, this one was pretty good. Less preachy than book 2, and back onto the original story track. I've heard this is the last book in the series, but the overall story didn't come to much of a conclusion. I had high hopes for this series, but in the end the first book is the only worthy title. Among other disappointments, the "prequel" was never tied in, just mentioned on the last page of book 4 as an afterthought.
 - Jeanne DuPrau)
