Dexter: Original Sin season 1 episode 10 ending explained: What happened with Nicky Spencer?

Dexter: Original Sin season 1 ended with episode 10, titled Code Blues, which aired on February 14, 2025. As the season finale, the episode was packed with twists and a setup for what's next in Dexter Morgan's dark journey.

The episode of this prequel focused on Brian Moser's troubled past, Dexter's struggle with his dark urges, and Harry Morgan's efforts to guide his adopted son. Meanwhile, the mystery of Nicky Spencer's disappearance reached a turning point. As Dexter uncovered the truth about what happened to Nicky, he found himself racing against time to save the young boy.

Things took a turn when it was revealed that Captain Aaron Spencer, Nicky's supposed father and a high-ranking Miami Metro officer, was behind his attempted murder. Spencer, furious after discovering that his ex-wife had lied about Nicky being his son, tried to drown the boy in a water tank on an abandoned barge.

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Dexter: Original Sin season 1 episode 10: Did Nicky Spencer survive?

Dexter Morgan (Image via Paramount Plus)

Yes, Nicky Spencer survived because Dexter acted fast. When Dexter found the boy chained inside the flooding tank, he immediately jumped in to save him. As the water kept rising, Dexter used an iron bar to break the chain. But Nicky had already swallowed too much water, so Dexter had to give him mouth-to-mouth CPR to bring him back.

Once Nicky woke up, Dexter fired a flare into the sky to signal for help. This ensured the boy got the medical care he needed. As Dexter watched Nicky being taken to safety, he quickly turned his attention back to Aaron Spencer, who had escaped.

But why did Aaron try to kill Nicky? It turned out that Aaron had just found out that Nicky wasn't his biological son. His ex-wife had lied to him for years, making him believe he was the boy's father. Filled with anger and betrayal, Aaron decided to get rid of Nicky by drowning him in the water tank.

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Dexter: Original Sin season 1 episode 10: What happened with Aaron Spencer?

Aaron Spencer (Image via Paramount Plus)

Aaron Spencer met a gruesome end at Dexter's hands. After making sure Nicky was safe, Dexter tracked Spencer to his ex-wife's home and confronted him late at night. Dexter used the same Etorphine hydrochloride to make Spencer unconscious.

Once Spencer was knocked out, Dexter took him on the boat that he borrowed from his colleague, leading him to Dex's victim bed. Following his Code, he gave a chilling speech about justice before cutting Spencer's body into pieces and dumping them into the ocean. He was careful to make sure no one would ever find the remains.

Afterward, Dexter went home and talked to Harry about what happened. Even though Dexter had killed Aaron, Harry was proud of him for saving Nicky and getting rid of a corrupt officer. This moment shows the strange moral code between them as Harry continues to see Dexter’s killings as a form of justice.

Meanwhile, Maria LaGuerta started getting suspicious about the recent murders in Miami. As she looked through the evidence, she noticed things didn't add up. Harry brushed off her concerns, but LaGuerta's instincts told her something was wrong.

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Dexter: Original Sin season 1 episode 10: Why did Brian Moser attack Harry?

Harry Morgan holding a gun on Brian Moser (Image via Paramount Plus)

Brian Moser attacked Harry because he was angry and felt abandoned for years. The episode showed that Brian had killed a woman named Barbara, who was her adoption officer, which led to a police investigation. At the crime scene, Harry noticed Brian watching from a distance, confirming his suspicion that Brian was the killer.

Harry confronted Brian in a tense and emotional conversation. Brian was furious that Harry had taken Dexter away from him when they were kids. He accused Harry of brainwashing Dexter, making him forget his past. But Harry defended his choices, saying he only wanted to give Dexter a fresh start, free from pain and darkness.

Brian refused to listen. Instead, he knocked Harry out with his gun but didn't kill him. Before leaving, he wrote "You're right" in blood on the wall, a chilling message that hinted he might understand Harry's reasons but still couldn't forgive him.

The episode ended with a mix of eerie and heartwarming moments. Dexter, Deb, and Harry celebrated together at a restaurant as Dexter got promoted, and Deb was accepted into the Miami Metro Academy. It was a rare happy moment for the family. But outside, Brian stood watching them through the window, a haunting reminder that he was still out there, waiting for the right time to reunite with Dexter.

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Fans of the franchise can watch all episodes of Dexter: Original Sin season 1 on Paramount + Showtime.