I've read O Jerusalem before, but I think I enjoyed it more this second time through, possibly because I got to relish the storytelling this time through instead of breathlessly wondering what would happen next. It's one of Ms. King's Mary Russell/Sherlock Holmes books, and it's actually the fifth book in the series, although it takes place during the events of the first book, The Beekeeper's Apprentice. Someone recommended that I read O Jerusalem after Apprentice and before the second book, A Monstrous Regiment of Women, and I've done that on both my trips through the Russell/Holmes books. I've yet to read all of this series, but I was inspired to start the series afresh when I met Ms. King a few months ago at a book reading. I'm not sure it's best to read the books out of published order like this, but that's how I've done it, so oh well.
O Jerusalem follows Mary Russell and her mentor Sherlock Holmes to Palestine, where they seek refuge from a deadly enemy back in Britain while helping solve a mystery in the Holy Land. Since this is a mystery, I won't say much more, so as to not spoil things for anyone coming newly to this marvelous series. If you want to know more, you can read an excerpt and reviews here on Ms. King's site. I will only say that this book continues the exceptional relationship between Russell and Holmes and is an adventure worthy of them both. If you are a fan of the original Sherlock Holmes stories by Sir Arthur Conan Doyle, I highly recommend this series, as it is the best non-Doyle portrayal of the master sleuth I have ever read.