I must admit to you guys that after a huge disappointment that was the third book which I barely made through due to some of its nonsense, I didn't have high expectations for the Dexter by Design.
But Jeff Lindsay knows how to develop annoyingly entertaining characters which his readers can't help but love, and introduce us to the new set of characters, which are of course a threat to Dexter's hidden identity, and which his readers can't help but hate, because they want Dexter to keep his identity, and keep doing his own thing to all the monsters that live in Miami.
Anyway, Jeff's proven himself to be a great writer and writes truly great stories, and Dexter by Design just so happens to be one of them.
It's a better story than the first two, and much better than the third, and it will keep you up all night with its dialogue and twists and turns, rooting for Dexter Morgan, who for some reason has more lives than a cat, and Deborah who gets stabbed (sorry for the HUGE spoiler) , and sometimes even for Rita and her kids, Astor and Cody, Doakes, even though they'll annoy the heck out of you. I know that I was very annoyed.
I'd love to write something else and add another HUGE spoiler to ruin the story for you, but I'm too nice to do something like that to you, so I'm going to let you to figure things out on your own, and see if the ending was worth your precious time. ;)