Dexter has trouble focusing on taking pictures of the crime scene and Cassie's body because he's distracted by thoughts of Hannah. He finds blood under Cassie's nails and thinks it may be Zach's blood. Cassie's murder is very similar to the Norma Rivera case. Deb shows up to see how Dexter is handling Cassie's death, and also to ask if Hannah is still in town. She leaves the crime scene because she feels out of place, but promises to continue the conversation with Dexter later.
On the way to the lab, Dexter meets with Hannah on the docks to discuss securing her a passport. She doesn't think that's why Dexter is really there. He would give everything to have no feelings again. Dexter thinks Hannah needs to get out of Miami and she agrees.
At the lab, Dexter determines that the blood under Cassie's fingernails is indeed Zach's. He lies to Vince and says it's Cassie's own blood because he can't risk being linked to Zach. With this being the second innocent woman Zach has killed, Dexter feels it is a waste that his apprentice won't have a future. As Dexter leaves the office, Quinn stops him to talk about the murder. He notices that the murder of Cassie looks very similar to the murder of Norma. Quinn believes Zach is the the murderer and tells Dexter to keep an eye out for any clues pointing towards this.
Dexter meets with Dr. Vogel to discuss Zach. They both haven't had contact with him in days. They should have seen what he was capable of. While he is just a boy, he can't control his urges. Zach knows too much about Dexter and Dr. Vogel to be allowed to live. She doesn't think he will be easy for Dexter to kill.
Deb stops by Dexter's apartment to ask about Hannah. She wants to know if Hannah is out of their lives or still in Miami. Dexter helps Hannah out with her boyfriend: he just needs to get her a passport and she will be out of their lives forever. Deb wants to have her locked up, but Dexter thinks that if she is questioned again she will reveal all of his secrets.
On Hannah's boat, Dexter helps her finalize her passport. Having already found that Zach is in the Keys, Dexter invites Hannah to come with him so that he can keep her safe.
Deb asks her boss, Jacob Elway, if he is interested in making a lot of money. The bounty on Hannah is large and Deb believes that Hannah is in Miami. Jacob is very interested and they leave to look for her. Jacob and Deb show up at the dock and discover that Hannah's boat is gone.
Deb finds that Dexter is lying about where he is: she thinks he is with Hannah and wants to find them. Dexter is on his way, with Hannah, to kill Zach. He tells her how finding Dr. Vogel was like finding a new family member. Dexter explains how Zach was his student but he has already killed two innocents and can't follow the code. Dexter never tried to find Hannah after she escaped because he likes to know she is still out there.
Hannah and Dexter eat lunch on the beach and discuss the names Dexter has for his targets. He insists that he only refers to her as Hannah. A police car shows up and causes Hannah to feel uneasy.
Upon reaching the hotel that Zach is staying at, Dexter tells Hannah to wait in the car while he picks the lock. He enters a room covered in plastic wrap with a set of knives very similar to Dexter's on the bed. A vision of Harry asks if Dexter must do this. Dexter says that he will use this very room.
Quinn meets up with Cassie's boyfriend, Oliver, to question him about Zach. After looking at a picture of Zach, Oliver thinks he looks familiar but doesn't know who it is.
At the hotel, Dexter grabs Zach when he enters his room. Dexter asks why he killed Cassie but Zach doesn't know who she is and says he went after Shawn Decker. Shawn is a guy he went to high school with who brags about killing a girl. Zach proves that he wasn't there for Cassie's death by showing Dexter the timestamps on his photos. Dexter is amazed that Zach follows the code without even knowing it. Dexter teaches Zach all of the things he did wrong with the killing. The two of them leave to dispose of the body while Hannah cleans the hotel room.
After Hannah throws out all of the plastic wrap, she returns to the hotel room to be ambushed by Deb. Deb asks what is driving Hannah, and she replies that Dexter is. Hannah tells Deb that she only kills people when she is left with no other choice. Deb planned on arresting Hannah but she doesn't want Dexter to get hurt so she lets her go.
In his car, Dexter has a vision of his father who says that Hannah is a distraction, or may be a desire stronger than the need to kill. Back at the hotel, Deb tells Dexter that she doesn't want to know anything else and leaves Hannah to him.
Dexter brings Zach to Dr. Vogel's house to tell her that Zach will stay alive. She spots Hannah in the car and insists that Dexter bring her in for supper. While they are eating supper, Dr. Vogel tells Hannah that the greatest danger is boredom. Her patients, who are always interesting, make life worth living. She never would have imagined Hannah and Dexter's feelings toward each other could be possible. She thinks they make a good couple but a bad one, too. Dexter still has Cassie's murder on his mind. He shows the rest of them the photos he took from the crime scene. Dexter suggests that Zach's blood was under Cassie's nails because someone is trying to frame him.
Deb returns to her office and Elway confronts her. He asks where Hannah is and why Deb doesn't seem interested in finding her anymore. Elway reminds her that a lot of money is on the line. Deb says she's not in it for the money and doesn't think she makes for a good investigator. She thinks of going back to the police but Elway warns her that the jobs are riskier and pay less.
Having left Vogel's, Hannah has a hard time saying goodbye to Dexter again. He wants her to tell him where she is going after she leaves the country. She agrees to tell him when she figures it out. Dexter explains what she should do when her plane lands but she interrupts him with a kiss. They both say he should go but they instead get undressed and spend the night together.
Dexter arrives back at his apartment and finds Zach dead in a chair. He turns him around to reveal a portion of his brain is missing. At Dr. Vogel's house, she holds a jar with Zach's brain in it, revealing that the brain surgeon is still loose.
The next morning Dexter stops Hannah as she is about to board her plane. He asks her to stay in Miami and she hugs him, agreeing to stay.