I wish the season finale had went that direction that could have set up a very interesting Season 6:
"Refusing to let Lumen leave his life, Dexter injects her with a sedative and goes to extreme lengths to restore her Dark Passenger while holding her captive. He starts looking for potential victims whose crimes could stir up Lumen’s hunger for retribution that she once had with Jordan and his rape group."
It could have been a way to go back to exploring the darker side of Dexter who's reached the breaking point after going through his share of disappointments and failures with other people he thought he had a connection with like Miguel and Lila. It could have also been a way to give the Dexter/Lumen relationship that bent, passionate craziness I was talking about and mold it into having that terrifying Macbeth vibe Temis the Red-Nosed Vorta
was talking about a while back.