What is the plot?

The query appears to mix two different shows: Green Sea: Millenium and Millennium. The search results provided do not contain any source material for a 2023 TV episode titled Green Sea: Millenium, Season 1, Episode 3, so I can't give a factual beat-by-beat spoiler for that episode from the available evidence.

If you meant 3 Body Problem Episode 3, the episode begins with Jin and Jack entering the VR game together and moving through a series of increasingly strange historical environments, starting with Tudor England, where Jin is immediately executed. They continue deeper into the game, and the story shifts to a desert setting in the Mongol Empire, where they see the world's instability firsthand and start to understand that the planet they are observing is trapped in an unsolvable three-body system.

As they keep playing, Jin realizes the game is not asking them to solve the three-body problem in the mathematical sense, because there is no stable solution for the planet's orbit. Instead, she understands that the true goal is to save the inhabitants of that doomed world. The game advances after that realization, confirming that she has identified the intended objective.

Afterward, Jin and Jack are invited to a summit in London and arrive at what turns out to be an empty venue, where Tatiana is waiting for them. She explains that the people behind the game are connected to a distant alien civilization known as the San-Ti, and that the headsets and game are being used to tell their story and recruit or test humans. Tatiana also makes it clear that the San-Ti are drawing closer, and she invites Jin to join the larger organization of Level 4 champions.

If you meant Millennium season 1, episode 3, the available results only say that the episode involves "the desperate search for a vicious killer" and that this investigation takes a toll on Frank and his partner, but they do not provide a complete scene-by-scene plot.

What is the ending?

In the ending, Frank Black and Jim Horn set a trap for the killer, and Horn, unable to stay back, follows the plan on his own terms and attacks the man when the van arrives. The police stop Horn before he can beat the killer to death, and Frank later tells him there is still enough evidence from the killer's house to convict him.

The ending begins with Frank and Horn working together on the final trap. They know the killer is targeting the optician next, so they use her as bait and wait for him to come. Horn is already fraying under the pressure, and as they wait, he admits that he cannot trust himself to remain at the scene. Frank tells him to go home.

Horn does not go home. Instead, he parks his car along the route to the trap and makes it look as if he has a flat tire. When the killer's van tries to pass, Horn lunges at him and starts attacking him. The struggle becomes physical and uncontrolled, and police arrive in time to stop Horn from beating the killer to death.

After the arrest, the case is not ruined. Even though the evidence from the van cannot be used in court because of Horn's attack, Frank tells Horn that investigators found enough evidence at the killer's house to secure a conviction. Horn has not been destroyed by the case, but he is shaken by what it has done to him, and he later asks Frank how anyone can keep working these kinds of cases day after day. Frank does not answer directly, and the episode closes with him at home comforting his daughter after another bad dream.

Frank Black's fate at the end of the story is that he remains active, composed, and still carrying the burden of the work, returning to his family after the case. Jim Horn's fate is more troubled: he survives, but he is left visibly strained by what he has done and by the violence he nearly carried out. The killer's fate is that he is stopped and left facing prosecution, since the house evidence is enough to support a conviction.

Is there a post-credit scene?

No. I could not verify any post-credit scene for Green Sea: Millenium, Season 1, Episode 3 from the available sources, and the results I found do not provide episode-specific post-credit information for this title.

The search results available here mostly point to unrelated materials: a DC post-credits list, older discussion of the 1990s TV series Millennium, and an episode listing/ratings page for that separate show. None of them document a post-credit scene for the 2023 episode you asked about.

If you want, I can help you verify this by cross-checking the episode's end credits, recap pages, or a scene-by-scene transcript if you can share one.

What specific case is Frank Black investigating in Episode 3, and how does the killer operate?

The available search results identify Season 1, Episode 3 as "Dead Letters" and indicate that Frank Black is pursuing a vicious killer in the episode, but they do not provide a detailed, scene-by-scene case summary from the source material available here. If you want, I can still help by turning this into a tighter, episode-specific question list based only on the evidence we do have.

What happens to Frank Black and his partner during the investigation in Episode 3?

One review summary says the search for the killer takes an unexpected toll on Frank and his partner, which makes their relationship and the strain of the case a likely focal point for Episode 3 discussions. The search results do not name the partner in that specific episode summary, so a more exact character-focused version would require fuller episode text.

Which victim or supporting character is most important to the plot of Episode 3, and why?

The results confirm that Episode 3 centers on a violent criminal case, but they do not identify the key victim or supporting character in the brief materials shown here. That means this is a plausible and specific fan question, but the available sources do not let me verify the exact character involved.

How does Episode 3 connect to Frank Black’s family or his personal life?

The season overview states that Frank Black lives in Seattle with his family and that the cases become increasingly more personal as the season progresses. Based on that season-level context, a character-specific question about whether Episode 3 affects Frank's family is more grounded than a general theme question, though the sources here do not spell out the exact family subplot for this episode.

What is the role of the Millennium Group in Episode 3?

The season overview says Frank works with a mysterious organization called the Millennium Group and that he investigates cases with its members, so viewers often ask how that organization factors into specific episodes. The Episode 3 result does not describe the Group's precise involvement in this case, but it does support asking about whether they influence the investigation.

Is this family friendly?

No -- this episode is not especially family friendly for young children, and it may be unsettling for sensitive viewers.

Potentially objectionable or upsetting elements include: - Nightmares and frightening imagery: a child has a disturbing dream involving a crazy clown with an upside-down face and an eerie staircase scene. - Psychological distress: the episode includes waking in terror, crying, and fear-based tension centered on a child's nightmare. - Dark thriller content: the episode is described as involving a vicious killer and an investigation with a stressful, ominous tone. - Emotional unease around family themes: the story appears to connect the case with Frank's home life, which can make the tension feel more personal and intense.

If you want, I can also give a kid-suitability rating by age range in the same spoiler-free style.