Well, rfisher, if you want to know what happens to Archie and Gretchen, here ya go. If ya don't, just scroll on by.
After multiple twists, turns, convoluted plot points and assorted eyerolling moments (this is a pun of sorts, although you'd have to read the book to get it), Archie has the chance to kill Gretchen, but to do it, he must let someone else die. Since he believes that the dying man in a serial killer, he does let him die, and instead stabs Gretchen with a scalpel she had been using to torture the dead man. Gretchen then tells him that the dead man was innocent, a victim of her plot to be MORE than a boring serial killer. She wanted to do something more challenging, like create evil in someone who isn't evil. Archie pulls his gun, puts it to her head, and wants very much to pull the trigger, then puts Gretchen under arrest and immediately feels redeemed because he hasn't become evil after all. He feels free for the first time since he met her. There's more to this scene, but those are the pivotal parts--well, it does sort of come out that Gretchen actually cared about Archie when they were having their affair and tortured him because she thought he was planning to break off their affair and stay with his wife, blah blah blah. Gretchen is arrested and carted back to prison, and Archie wanders off into the sunset hand-in-hand with Susan, the young reporter with the colorful dye jobs.
So the possiblity exists that there will be MORE books.
In the grand tradition of rapidly produced series fiction, the first one was the best of the lot and the last one was the worst. And I think the main reason this series is so creepy is that Chelsea Cain seems to be very much in love with Gretchen herself.