This week we finally learned the name of that scared girl who watched Dexter kill Boyd with a kitchen knife: Lumen Anne Pierce. We also got a piece of her backstory, which includes a mother who understands why she would have to leave her home in Minnesota, and, more importantly, the fact that there were others (besides Blyd) who tortured her.
Though Dexter has dealt with unwanted witnesses before, he’s never dealt with anything like this before. He should kill Lumen, and it would be easy since no one is looking for her, but he can’t.
Dexter realizes that he has to convince her that she is safe with him or she is going to keep trying to run and may eventually find someone to tell what he has done. At first, he tries to restrain her, but she she fights back , smearing blood all over him and forcing him to sedate her. Just then, Deb calls him to a crime scene, where she has been all night, meaning no one came home to relieve the nanny.
By the time Dexter gets back to the apartment, the nanny is pissed and quits.