This book was written by Shelly Dickson Carr and published in December, 2013. I don't see a review of this book on these boards; forgive me if there is one.
I bought this book not realizing it was for teens. It was full of inaccuracies, but it obviously is fiction and so that didn't bother me. There is a strong female lead; kind of like Nancy Drew meets Jack the Ripper. Amazon tells me it won a number of awards for teen mystery/suspense.
Despite the fact that I'm not - nor ever have been - a 15-year-old girl, I found this book enjoyable. The author skillfully uses Cockney rhyming slang (at least to my knowledge or lack thereof). The second half of the book, in particular, is great. Carr crafts a real whodunnit: Although there is an obvious red herring, she neatly arranges things such that about five others plausibly could be the Ripper (had access, motive, etc.). I didn't figure it out until it was revealed. When it was, I was impressed that it was fair; the clues were there and the solution was reasonable.
I recommend it. You have to get past the time travel bit, and the first few chapters are slow, but it is worth the read, especially if you are, like, a teenager.