"Beauty and the Beast"
The episode's title is a reference to Dexter being the "Beast" (as he is a killer and is somewhat possessed with a Dark Passenger), and Julia Stiles' character, Lumen, being the "Beauty" (as she is innocent, young, and a woman).
In this episode we learn many things about Lumen, but even more about Dexter--that he has changed from being a cold, lonely serial killer to a loving parent who wants to form relationships and have a family. Dexter in himself is a kind and caring individual to those that are justifiably innocent in terms of his strict Code, and he generally wants to do good. The whole means of justifying his killing is a sense of vigilantism mingled with what he deems as justice, and his Code is one that is meant to protect the good and the right. It is no surprise, to me at least, that Dexter would eventually evolve in this way and move on to want to create his own family and children--to be able to harness and behold the innocence in which he protects and shields with his acts of violence (except, ironically, at the end of Season 4 where Rita is killed by Trinity simply because she's Dexter's wife).
Basically, if Dexter didn't have a means of justifying his reasons for killing, he would most likely believe that he was no different than those who murder and commit crimes. It's important for him to seperate himself from those that he kills in this way; by having a family, he reasserts his justification by having the innocent, those that he kills to protect, around him. By having Lumen and Harrison, Dexter is allowed a sense of tribute to his deeds, as those that are innocent are protected by his killing of murderers.
Dexter learns more about Lumen's life and consequently forms a bond with her by showing her the remains of Boyd Fowler's other victims, saying that she, too, would end up like all the other girls. Lumen realizes that Dexter had saved her, and she warms to him--I hope that she takes Rita's place and acts as a central of a nuclear family.
Also Dexter wouldn't be able to survive as a single dad without the help of his nanny (who's name I can't remember, kind of embarrassing, heh). Hopefully Lumen will help out with Harrison, too, and perhaps act as Dexter's love interest.
Also I believe that Lumen can act as a means of Dexter's retribution, as she has been tortured and harmed by others--the killing of those that have hurt Lumen, that have robbed her of her innocence (as Dexter's had been taken away when he was a small child, and the way that Harrison's had as well), he will redeem himself with revenge and cleanse Lumen of her psychological scars. By doing this, Dexter will feel whole again, and feel as if he has done something meaningful.moreless
