I liked the first in this series, but Seven for a Secret is much better. I think it helps that it's a novella, rather than a novel made out of novellas, if that makes any sense - it feels more cohesive, more stripped back, and I've always liked novellas anyway. Vampirism takes a backseat here to werewolves, and adolescent girls turning into werewolves, or their berserker equivalents, will never not entertain me. Ruth, especially, is an excellent character, and while readers never get to see her eventual assassination of the Prussian chancellor, I don't think that we need to. It's enough to know that she gets it done. 

As I said, I liked the first book, but this is the one I'd read again.