The police team attempt to get Christine Hill to talk while Dexter frames another man in order to get Arthur Mitchell, The Trinity Killer, all to himself, however it is also the episode where Arthur learns that Kyle Butler is really Dexter Morgan, and learns about Dexter's life as a blood spatter analyst.
The episode begins with Christine Hill under interrogation by Angel Batista. Angel asks her about her parents and tries to get her to give him a name, which spurs Dexter to think about framing someone as a decoy to the police, giving him time to kill Mitchell. Mitchell sees the news of the return of the boy he abducted and realizes that Dexter had not told the police about him. He phones Dexter and asks what he wants; Dexter, improvising, tells him that he wants $50,000, or he will tell the police that Mitchell is a pedophile. Dexter tells him that he has 24 hours to get him the money. Mitchell takes out a phonebook and researches the various Kyle Butlers of Miami and tells Dexter that he will be in touch.
Back at the station, Debra tries to get Quinn to start thinking properly and see that Christine isn't who she told him she was. Dexter leaves the station, which Quinn reacts suspiciously, asking him where he's really going, after Dexter tells him he's going to see Rita for lunch. Captain Matthews informs LaGuerta and Batista to meet him in his office. He shows them a video of the two kissing, which proves they were lying in their affidavits; he tells them that they have committed perjury, and are going to need to find new jobs. Dexter goes through possible victim files to decide which one he should frame for Trinity's murders. Meanwhile, Arthur gets caught trying to break into a house by a man named Kyle Butler who tells him that he will call the police. Arthur proceeds to kill him offscreen. Dexter arrives for an appointment with Rita for marriage counseling, but gets called to a crime scene as soon as he arrives, soon after, Rita confesses that she and Elliot kissed.
Dexter arrives at his crime scene, which turns out to be Kyle Butler, which makes Dexter realize that Arthur is after him. Meanwhile, Batista and Debra search Christine's apartment and find a collection of postcards among her shoe boxes, from her father. Dexter goes to another Kyle Butler and renders him unconscious via injection, in order to catch the Trinity Killer, but as soon as Mitchell comes through the door, he realizes that it is not Dexter and leaves before Dexter can grab him. Batista, having returned to the station, shows Christine the postcards and after pressuring, she requests her lawyer. This makes Quinn realize that she was using him to get close to the case. Debra tells him not to beat himself up, telling him that she knows what it feels like, having been similarly manipulated by Ice Truck Killer. Dexter arrives at the home of Stan Beaudry and realizes that he has taken a trip to Jacksonville. Dexter nearly drives away, but his mental vision of Harry tells him that he has a wife that he needs to return to. Dexter goes home and talks with Rita, forgiving her offhandedly for kissing Elliot, as if it did not matter; for her part, Rita is concerned that Dexter may not appear to care that she nearly cheated on him.
Dexter is called into the station and Debra attempts to get Christine to talk, she tells her about her issues with her father, Harry, but Christine reveals nothing. Dexter arrives at the station and acts as witness to LaGuerta and Batista's marriage. He rushes off soon afterwards to kill Stan Beaudry. After a phone call from Mitchell, he catches up with Beaudry and kills him rapidly and plants Arthur's DNA and a picture of Christine in his truck and goes back to his home and plants a hammer there. Dexter returns home and punches Elliot in the face for kissing Rita; she witnesses it and prepares some ice for his hand, telling him that she is glad that he cared. LaGuerta and Batista inform Matthews of their marriage, telling him that a perjury charge wouldn't stand up in court. Christine calls Mitchell to tell him that she's in trouble, and he angrily tells her to never call him again. Meanwhile, the team finds all the evidence Dexter planted. Debra and Quinn rush to Christine, believing that she wishes to confess. She tells Debra that she shot her and killed Lundy, and asks Debra to forgive her. When Deb refuses, Christine pulls a gun from under a cushion and commits suicide.
After hearing a phone call from Mitchell, Dexter goes to the arcade game area to hunt for him, unaware that Mitchell is in fact following him back to the station. Mitchell infiltrates the station by stealing a visitor's badge and wanders around the station, looking at his work. Debra tells Dexter that she is afraid to erase Lundy's name from the board because then it will all be over. Debra wipes it off after some thought and Dexter goes to his office. To his horror, he sees Mitchell headed toward his office; Arthur looks at Dexter's ID badge and says "Hello... Dexter Morgan".
- The final scene is sometimes regarded as being the best scene of all time in Dexter, along with the scene where Dexter thinks up ways to tell his sister that he's The Bay Harbor Butcher.
- IGN gave the episode a "Great" rating of 8.8/10 and said of it that: "We all know that Lithgow's been amazing this season, but I wanted to once again call out Jennifer Carpenter's performance as well. She was given a strong storyline that truly fit with her character's manic energy and she's nailed every scene like a conquering hero. Her hesitance to erase Lundy's name from the case board at the end was great, and so was her realization that focusing on work didn't wind up filling the void in her life; that solving the case didn't bring her any closure. "I knew finding his killer wouldn't bring him back," Deb lamented. "But I thought it would bring something." I'd also like to take the time to bring up Courtney Ford's Christine Hill. Let's face it. Ford is fairly flat as an actress, but her best work definitely came in these past two episodes when she had much more difficult scenes to work through. Who knew that she would wind up being worlds better during moments of heartache and anxiety than she would just saying rudimentary lines like "My name is Christine and I'm a reporter"?"
- "Hello, Dexter Morgan" was nominated for a Primetime Emmy Award for Outstanding Sound Mixing for a Comedy or Drama Series. The nominees were James P. Clark, Elmo Ponsdomenech, Kevin Roache and Jeremy Balko.