Update to my review:
Apparently this is not the conclusion of the series, but there is no information yet on future releases. My review still stands, but I thought I should clarify!
I loved this conclusion to the Charlie Madigan series, an interesting foray in the urban fantasy world. If you have read the first three you should jump on this right now. I will give one caveat though, if you have been reading the books as they are published, I would highly recommend a re-read. Book 4 continues pretty soon after book 3 ends, and I think I would have enjoyed this even more if I had done that, because alot of the things that have happened in the past are important here.
I really hate rehashing plot lines, but the heroine Charlie lives in Atlanta where she is a police detective, on a special task force that deals with the interaction between earth and 2 off-world species Elysians and Charbydons. Charlie's partner Hank (a siren) was abducted at the end of the 3rd book and taken to Elysia, and Charlie is on a mission to rescue him.
I can't go into any greater detail without huge spoilers, so I won't. What I really did like though, is the special power of sirens is their voice (gives talking during sex a whole new meaning!)