2nd in the Vampire Files series by P.N. Elrod...
Before I get to the actual plot stuff I have to share a weird connection in this book. Near the beginning of the book a couple of the characters go to see a movie version of Romeo and Juliet, since the book is set in the 30's that means it must be this version from 1936. Here's the nifty bit... the actor who played Friar Laurence in that version, Henry Kolker, is a relative of mine! I don't remember what the relationship is exactly off the top of my head, but I think he's either a cousin a couple times removed or a great-great-great uncle or something like that. I'll have to look it up. That completely tickled me when I realized it while I was reading and I had to share.
Plotwise... the sister of the vamp that turned Jack shows up and she's very old and sick now and wants him to turn her. There ends up being a touch more character stuff than there was in the first book (which I appreciated since I like character stuff).