Again, Dexter is forced to let down some people, making his job as an excuse. Dexter and Jordan had a little mind game through a phone call. And back at the station everyone was lured to the crime scene of Liddy's murder. LaGuerta found out that the last call that Liddy made was for Quinn and she noticed the blood on his shoe. Quinn was made the prime suspect and he demanded lawyer.
Dexter managed to break away from the crowd, stealing a red car to find the place where Jordan kept Lumen. The psychopath was torturing Lumen but she appeared to be much stronger than the first kidnapping. Dexter found the place but crashed his car and woke up to find that he's been tied inside the summer camp house.
Dexter got himself free, stabbing Jordan in the foot and laid him on the table. He let Lumen finish Jordan and she took the chance pretty aggressively. Before the job was done, Deb came to the scene after a tip from the fruit vendor. She told Dexter and Lumen to freeze but actually did not see who they were behind the translucent plastic.
Deb had an understanding that these two people are vigilantes who have wiped clean people like Jordan, so she let them go before calling in the station to inform the murder. Dexter and Lumen quickly finished their job and returned to their respective places. Cut to Quinn who was given the benefit of the doubt by Deb. Seeing how much Quinn made Deb happy, Dex botched the blood work that freed Quinn from the charges.
Dexter had a happy scene at Harrison's birthday party and that is after Lumen told him that she's done with her Dark Passenger. She was leaving the town to start new.
Executive producer Sara Colleton explained the final decision to let Lumen live. "From the very beginning we knew that Lumen would leave Dexter," she said. "...Their respective traumas have created this bond. So it's devastating for Dexter to lose her, and he has never wanted anything before like this. But at the same time there's something so incredibly direct about Lumen that when she tells him why she has to leave, it makes perfect sense to him. He understands that her dark passenger has left, that her need for vengeance has been quenched, and that he can never escape this, this is who he is, and he needs to let her go. As he said, 'I will carry your darkness with mine'."
Colleton also confirmed that the possibility of Julia Stiles reprising her role is open wide. Speaking of the next season she said, "Deb will learn Spanish, I think Harrison will be seeing his second birthday, and Dexter will still be enjoying the Slice of Life." Other explanations including why Deb did not open the plastic curtain to find out the killers are at EW.com.
