It's week three of the Bay Harbor Butcher investigation, and all of Miami is suffering through a heatwave. Rita tells Dexter that her mother is coming to town to visit, both to show support after Paul's death and to patch things up with her daughter. Cody is starting to have nightmares about the BHB, but Dexter assures him that only people who do bad things should be afraid of the Butcher.
At the station, the task force begins re-examining the case with the new knowledge that the Butcher's victims are all criminals. When Masuka confides in Dexter that he may have made a major break in the case, Dexter becomes increasingly paranoid that he'll soon be found out. He visits Lila in an attempt to clear his head. As they drive around together, Dexter gets a glimpse of Lila's unusual nature; she runs over a street post, then steals some wind chimes. According to Lila, this is "found art".
Dexter gets called away to a crime scene; a woman has been shot and killed, apparently by her husband, Curtis Barnes. Doakes immediately recognizes the precise method of shooting as special-ops and decides to take the lead on the investigation. Dexter finds it difficult to focus on the blood spatter analysis at hand and can't help asking LaGuerta and Doakes for details on what exactly Masuka has found.
Back at the field morgue, Lundy and the task force puzzle over three of the Butcher's victims who have no criminal record and therefore do not fit the pattern. Angel is put in charge of investigating one of these victims, a man named Oscar Sota.
At the station, Doakes makes a few calls and manages to arrange for a meeting with a friend of Barnes from his old unit. Meanwhile, Pasquale's continued preoccupation with her fiancé's cheating presents Dexter with an opportunity to delay the task force's investigation; when Pasquale asks to have her fiancé's shirt forensically tested for the smell of a woman, Dexter points her in Masuka's direction, hoping it will burden him and keep him off the Butcher's trail.
Rita's mother Gail arrives at the house, and while things appear to be tense, she seems to want to reconcile with Rita. Dexter drops by for dinner and meets Gail. He feels uneasy when she starts asking him questions, but is surprised to find that she also approves of the Butcher's activities.
After hours at the station, Lundy and Deb are still poring over the evidence. Lundy reveals that he has a date that night and advises Deb to also get away from work and pursue a personal life. At the gym, she meets the boxer Gabriel again. Taking Lundy's advice to heart, she brings him back to Dexter's apartment for sex, handcuffing him to the bed, because as she says: "The last guy I had sex with tried to kill me." Dexter comes home early and walks in on them, assuming Deb was just on the treadmill as usual.
The next morning, Deb and Dexter talk about the BHB case, and Deb reveals that Masuka's big break is actually something very small: microscopic algae found inside the body bags, which might be used to pinpoint the marina in which the BHB keeps his boat.
At the station, Angel interviews the wife of Oscar Sota. The wife refuses to believe that her husband was a murderer, even though his body was found with 13 other confirmed killers. Frustrated, Angel demands that Mrs. Sota reveals more details about her husband. She refuses and storms out.
Doakes leaves the station to meet up with Barnes' friend at the marina, only to find that it is Barnes himself. Barnes is under the impression that Doakes, as a brother in arms, is willing to help him escape. However, when Barnes admits to have killed his wife, Doakes attempts to arrest him. Both men draw their guns on each other, creating a tense standoff.
At the station, Lundy tells Deb that his date the previous night was a disaster. Deb sympathizes and proudly shares that she also "got laid" last night. Seeing that Lundy is unimpressed, Deb is embarrassed. Lundy reveals that he has little hope of having another romantic relationship, since he believes his shot at a beautiful relationship has already passed. In the lab, Masuka seems to be zeroing in on the algae lead, and a marine biologist is being brought in to help with the analysis. Pasquale confronts Masuka, angry that his forensic tests on her fiancé's shirt revealed nothing. She has an emotional breakdown in front of the entire station, and LaGuerta comforts her.
Back at the marina, Barnes and Doakes discuss their common experience of being a Ranger. Barnes explains that the psychological damage he endured on his special-ops missions made him a difficult person to live with, and that eventually his wife couldn't take it anymore and was about to leave. Doakes reveals that he had the same experience, but had decided to end the relationship himself, before he turned violent. Barnes tries to get Doakes to flee to Cuba with him, but Doakes refuses and says Barnes must turn himself in. Barnes refuses and draws his weapon again; Doakes is forced to shoot and kill him.
At lunch with Lila, Dexter tells her he no longer wants her as a sponsor. In a flashback, we see a young Dexter being asked a series of psychological profile questions. Following Harry's advice, Dexter answers with the exact opposite of what he feels, managing to pass off as normal. Back in the present day, Dexter abruptly leaves Lila at the lunch table.
Captain Matthews visits the station. In the wake of Pasquale's meltdown, Matthews has decided to reinstate LaGuerta as head of homicide. LaGuerta continues to voice her support of Pasquale, but eagerly accepts the promotion.
Outside the field morgue, Dexter concocts a plan to destroy the evidence inside; he hopes to somehow use the unusual heat wave to "melt" the bodies. Lila shows up in the parking lot, refusing to accept Dexter's rejection. She asks Dexter why he seems to be so afraid to discuss his inner monster and claims that he labels himself a monster to escape responsibility for his actions. She does not believe that a person can be entirely evil. To prove her wrong, Dexter brings her into the field morgue to show her the gruesome products of his own evil. To his surprise, she is not horrified or repulsed, but rather fascinated. She believes that the Bay Harbor Butcher, like all people, is neither completely evil nor completely good. Lila seems to see Dexter clearly, in a way that not even Harry could. In another flashback, Harry praises a young Dexter for fooling the doctor and being able to hide the monster inside him. Dexter is visibly hurt by this.
Back in the parking lot, Dexter muses to himself that, despite all the pressure he's under, Lila is able to make him feel okay about who and what he is. Dexter agrees to continue being sponsored by Lila. She hugs him and kisses him on the lips.
Angel visits Oscar Sota's widow at her house, this time to apologize for his rudeness when interviewing her. He confesses that he was so tenacious because he wanted Sota to be a bad person, since it would help him to make sense of all the murders. The widow accepts his apology and then confides that her husband hid several guns in the walls. She invites Angel inside.
That night, Dexter puts his sabotage plan into action. As the garbage truck drops off a dumpster next to the field morgue's air conditioning unit, Dexter kicks and damages the unit to make it look like it was the fault of a careless garbage man.
At the gym, a television screen shows a news anchor voicing his opinion that the Butcher is doing a good service for the city and should be praised. Deb runs into Gabriel again, and this time she asks him out on a real date. Gabriel accepts.
Someone else is watching the news program: LaGuerta. As she stares at the TV screen, a man is shown in bed with her; it is Bertrand, Pasquale's fiancé. LaGuerta tells him it is the last time she'll see him, and he should go back to Pasquale. Bertrand calls her a cold-hearted bitch, realizing he was being used for LaGuerta's political purposes.
The next morning at Rita's house, Dexter tells Rita he has reconsidered and wants to keep Lila as his sponsor. Rita reluctantly accepts this. As Dexter starts playing with Cody (who is now dressed up as his favorite hero, the Butcher), Gail tells Rita that she senses Dexter is hiding something, and that he is very good at hiding it.
At the field morgue, Lundy, Masuka and the marine biologist walk in on a sickening scene. The bodies, having spent all night with hot air being blown over them, have started to liquefy and are now completely useless as evidence. Dexter is barely able to hide his relief as he discusses this latest development with Masuka. However, his good mood is short-lived, as Masuka reveals that the algae evidence was stored separately and was unaffected by the heat. The algae being analyzed were not found on the bodies themselves, but on rocks that Dexter used to weigh down his bags. Masuka tells Dexter that the results should be available in a week. The camera fades out as Dexter begins contemplating which method of execution he would prefer.