Dexter is back with New Blood, but the original series still sets the bar. Fans will have little trouble recalling their favorite colorful phrase from Deb or which 'big bad' of the season haunted them the most (the answer is Trinity, hands down).
However, some of the most interesting scenes in of character and story development occurred with guest stars who appeared in one only episode, yet triggered major changes in characters and reactions in the audience. Each of them made their short time on screen pack a punch like one of Dexter's tranquilizer shots.
Nurse Mary - Season 1, Episode 3 - 'Popping Cherry'
Nurse Mary is Dexter's first "playmate," and his interaction with her is a defining moment for Dexter's character. He had to have a 'first,' but her character is unusual because she isn't a random escapee from justice; she is trying to kill Harry. All Dexter's efforts to kill her show his inexperience. By highlighting Dexter's awkwardness and desire to protect Harry, this murder strangely humanizes him. Dexter's scenes with Nurse Mary are unforgettable because they mark the full birth of Dexter's Dark enger.
Dr. E. Meridan - Season 1, Episode 8 - 'Shrink Wrap'
There are many great points in Season 1 of Dexter, but Dr. Meridan stands out because he reassures Dexter that everyone has "a big bad wolf inside." Dexter believes he is incapable of feeling, but when he confides in Dr. Meridan, he is treated like a 'normal' person with regular problems. More sessions with a serial-killer doctor analyzing a serial-killer patient could have been fun, but Dexter killed him after only a few visits, indicating that Dr. Meridan struck a nerve. Though he ends up on Dexter's table, he still gives Dexter valuable advice - that he isn't as separated from the rest of society as he thought.
Joey - Season 2, Episode 2 - 'Waiting To Exhale'
Joey steals his scene in with an unforgettable interaction with Deb. Normally unfazed by insults, Deb loses control when Joey taunts her about Rudy and points her gun at his head. Angel's shock mirrors the audience's reaction, underlining in bold just how deeply Deb has been traumatized by the betrayal. Viewers witness her going over the edge, crossing the line between protecting the community and terrorizing it in a few seconds. Joey's urine-soaked pants are a wake-up call for Deb on how desperately she needs to care for her mental health.
Nathan Marten - Season 3, Episode 3 - 'The Lion Sleeps Tonight'
Nathan's character asks the critical question - can Dexter break Harry's Code? Harry had always treated Dexter's desires as an illness, so initially, he identifies with Nathan's "uncontrollable" urges. However, Nathan is driven solely by his own pleasure, while Dexter uses his Dark enger to protect others.
Dexter's first deliberate tres against Harry's Code is in Nathan's killing, which sets him apart. The character also gives Dexter his first opportunity to act as a protective father after Rita announces her pregnancy. Even as Dexter tries to be the kind of father Harry would want him to be, he recognizes the need for carving his own path in his killing patterns.
Young Nanny Candidate - Season 5, Episode 3 - 'Practically Perfect'
Dexter is looking for a nanny, but Deb is the one conducting the interviews. The first candidate is clearly unprepared for Deb's interrogation. Deb's behavior scares her away while Dexter says nothing, highlighting the different walls both the Morgan siblings have built. The short interaction with the nanny candidate illustrates how paranoid Deb's past trauma has made her, along with her fierce desire to protect Harrison. Though other nanny candidates have brief scenes, the first one functions as an audience surrogate, confused and caught unaware by Deb. The scene also demonstrates how Dexter's lack of confidence in his connection to his own son.
Trisha Billings - Season 6, Episode 1 - 'Those Kinds Of Things'
Dexter makes a quick exit when Trisha first hits on him at their high school reunion. After all, even the best couples on Dexter usually don't have happy endings. Trisha doesn't give up, though. The make-out session they have is a rare example of Dexter telling his inner voice to shut up. For Dexter, who likes to plan out all human interaction, positive yet casual sexuality is a new experience.
Dexter doesn't need to hide anything about himself because Trisha expects nothing from him beyond that moment. She's an excellent one-episode character because it would destroy the point if Trisha returned for seconds. Dexter gets to exorcise bad high school memories and move past Lumen as far as physical memories, all in one encounter.
Walter Kenney - Season 6, Episode 3, - 'Smokey And The Bandit'
Fascinating character personalities are common on Dexter, but Walter, an old man who answers the door, drunk, in tightie-whities, drools over dirty magazines, and cheats at golf, is priceless. To Dexter, though, he is an anti-Harry figure, a killer that Dexter ired growing up. In Dexter's present, though, Walter's isolation from his family is a warning, reminding Dexter that what separates him from other serial killers is his relationships with others. However, even as he tries to reject the idea that he is anything like the "Toothfairy," when he drops his slides and they fall out of order, Dexter is reminded that his obsessive need for his trophies is just like Walter's, forcing him to take a hard look at his own behavior.
Wayne Randall - Season 7, Episode 2 - 'Sunshine And Frosty Swirl'
Trying to suppress his killing instinct, Dexter takes an interest in Wayne Randall's case. Randall's scenes all feature him in a prison jumpsuit and shackles, a constant reminder that Dexter's freedom is at risk. Randall is shown enjoying things Dexter takes for granted - the sun on his face, a cold ice cream cone. During Dexter's questions about Randall's change of heart, Dexter looks uneasy as he contemplates that maybe he could change if he truly wanted to. In addition to the interesting dialogue, Randall has a sudden death that made viewers sit up in surprise and makes it clear he will never return. Ultimately, Randall confirms Dexter's belief that killers don't change, despite the fact that viewers have been witness to many changes in his personality.
Donna Randall - Season 7, Episode3, - 'Buck The System'
Donna is unique as a single-episode guest star because she knows her son was guilty, doesn't try to make excuses for his behavior, and comes to assist the police of her own volition. Still, she held onto evidence to keep Wayne from the death penalty. Deb's questions about this point out the war inside of Deb between preserving evidence and protecting a family member. Donna is the outward expression of the inner turmoil that Deb faces and seeing her makes Deb rethink what she would do to keep Dexter free.
Miles Castner - Season 8, Episode 7, - 'Dress Code'
Miles Castner is all tightly-controlled anger and subtle menace. Though his accent is as smooth as his expensive suits, Miles demonstrates his possessive nature in very physical ways, such as standing between Dexter and Hannah. Dexter's reactions are similarly physical and show his concern for Hannah long before he its. Miles is such a threatening character that his presence lingers even he isn't on screen. Hannah's shaking voice and pleas for Dexter to leave underline how much Miles frightens her. Killing Miles in self-defense keeps Hannah sympathetic to viewers and clears the way for her reunion with Dexter, while Dexter's rush to protect her shows he would risk his own life to protect hers.