Now You See Me by SJ Bolton

This was an interesting psychological thriller, recounting the episodes of a "Jack the Ripper" copycat murderer.  On the anniversary of the original Jack the Ripper's first killing, a young detective, Lacey Flint, finds herself holding onto a dying woman while leaning against her car in East London, where the original murders took place.  She feels responsible for the woman's death because she was with her during her last breaths of life. Could she have caught the killer? The woman was still alive and her blood still warm and fresh!
Lacey soon receives a call from a journalist who supposedly got a letter from the killer and it shows that the killer is a Jack the Ripper copycat.
Lacey is somewhat of an expert on Jack and her knowledge becomes useful to the investigation.
Lacey becomes a suspect herself in the eyes of her nemesis, Mark Jonesbury, also on the case.
Throughout the book, it is clear that there is a link between Lacey and the murderer.  It turns out, also, that these murders have something to do with a set of twins and that Lacey is somehow involved.
I won't give any more away, but just say that it was a fast read - a good  mystery. Now on to more serious stuff!