The episode begins with a scene in the Starcourt Mall, where a group of teenagers, including Mike, Lucas, and Max, are enjoying their summer. They are seen hanging out, shopping, and having fun, but there is an underlying tension as they navigate their relationships. Mike and Eleven are particularly affectionate, while Lucas and Max are also growing closer. Meanwhile, Dustin is excitedly trying to impress his friends with his new girlfriend, Suzie, who he has been communicating with over the radio.

The scene shifts to the Byers' house, where Joyce is trying to cope with the strange occurrences in Hawkins. She is still dealing with the aftermath of the Mind Flayer's influence from the previous season. Joyce is determined to protect her family and is increasingly worried about Will, who has been experiencing disturbing visions and feelings of being watched. Will is struggling with the lingering effects of his past trauma, feeling disconnected from his friends and haunted by the memories of the Upside Down.

Back at the mall, the gang is interrupted by a sudden commotion. They witness a group of Russian agents, who are secretly operating in Hawkins, and they realize that something sinister is happening. The kids decide to investigate further, leading them to a series of clandestine meetings and discoveries about the Russians' plans. They uncover a hidden room in the mall that contains a large machine, which they suspect is connected to the strange happenings in Hawkins.

Meanwhile, Nancy and Jonathan are working at the Hawkins Post, where they are investigating a series of mysterious disappearances linked to the mall. They interview a local woman who has been affected by the strange occurrences, and their investigation leads them to a confrontation with their boss, who is dismissive of their concerns. Nancy is determined to uncover the truth, but Jonathan is more cautious, worried about the potential consequences of their investigation.

As the episode progresses, the focus shifts to the character of Billy, who is being manipulated by the Mind Flayer. He is increasingly aggressive and erratic, struggling with his own demons while being used as a vessel for the creature's influence. This internal conflict is highlighted during a tense scene at the pool, where he confronts his own feelings of inadequacy and anger.

The narrative then returns to the kids, who devise a plan to test their theory about the Mind Flayer's influence. They decide to use a sauna as a means to expose any potential hosts of the creature. They believe that the heat will force the Mind Flayer out of its victims. The group gathers at the Wheeler's house, where they prepare for the test. Mike, Lucas, Max, and Eleven are all present, and there is a palpable sense of anxiety as they discuss the risks involved.

During the sauna test, they manage to capture Billy, who is still under the Mind Flayer's control. The group places him in the sauna and turns up the heat, hoping to draw out the creature. As the temperature rises, Billy begins to struggle, and the Mind Flayer's influence becomes apparent. He experiences intense pain and confusion, revealing glimpses of his internal battle. The group watches in horror as Billy's body convulses, and they realize the true extent of the Mind Flayer's power.

In a climactic moment, Billy breaks free from the sauna, enraged and desperate. He attacks the group, and a chaotic fight ensues. Eleven tries to reach out to him, attempting to break through the Mind Flayer's hold, but he is too far gone. The confrontation escalates, and the group is forced to defend themselves against Billy's violent outbursts. Ultimately, they manage to subdue him, but the emotional toll of the encounter weighs heavily on everyone, especially Eleven, who feels a deep sense of loss for the person Billy once was.

The episode concludes with the group reflecting on the events that transpired. They are left with more questions than answers, realizing that the threat of the Mind Flayer is far from over. The tension between the characters is palpable, as they grapple with their fears and the uncertainty of what lies ahead. The stakes are higher than ever, and the bonds between the friends are tested as they prepare for the challenges that await them in Hawkins.

In the ending of "Stranger Things 3," the main characters face off against the Mind Flayer in a climactic showdown. Eleven, Mike, and the rest of the group confront the creature in the Starcourt Mall. They devise a plan to use a sauna to test for the Mind Flayer's presence, leading to a tense and emotional confrontation. Ultimately, they manage to defeat the creature, but not without significant personal losses and emotional turmoil. The episode concludes with the group feeling a mix of relief and sorrow as they grapple with the consequences of their battle.

As the episode unfolds, we find ourselves in the aftermath of the group's discovery of the Mind Flayer's influence over the town. The scene opens in the Hawkins Mall, where the atmosphere is charged with tension. The group--comprised of Eleven, Mike, Dustin, Lucas, Max, and others--gathers in the food court, their faces reflecting a mix of determination and fear. They know they must confront the Mind Flayer, which has been manipulating their friends and the townspeople.

The plan is set: they will use a sauna to test for the presence of the Mind Flayer. The group splits up, with some heading to the mall's sauna while others prepare to lure the creature out. The camera captures the urgency in their movements, the way they exchange glances filled with unspoken fears and hopes. Eleven, feeling the weight of her powers and the responsibility to protect her friends, steels herself for what's to come.

In the sauna, the tension escalates as they begin the test. The heat rises, and the group watches anxiously as they wait for a reaction. Suddenly, the atmosphere shifts; the lights flicker, and the temperature soars. The Mind Flayer's presence is felt, and panic ensues. The group realizes that they are not just testing for the creature but are also putting themselves in grave danger. The sauna becomes a battleground, and the stakes are higher than ever.

As the Mind Flayer attacks, the scene is chaotic. The camera captures the frantic movements of the characters as they try to escape the sauna's confines. Eleven, using her powers, fights back against the creature, her face a mask of concentration and fear. The emotional weight of the moment is palpable; she is not just battling a monster but also the fear of losing her friends.

Meanwhile, outside the sauna, the rest of the group is engaged in a desperate struggle against the Mind Flayer's minions, who are attacking them in waves. Lucas and Max fight valiantly, showcasing their bravery and determination. Dustin and Steve work together, their camaraderie evident as they strategize on the fly. The scene is filled with action, but it also highlights the bonds of friendship that have been forged through their shared experiences.

As the climax reaches its peak, Eleven channels her energy, and with a powerful surge, she manages to weaken the Mind Flayer. The creature writhes in pain, and the group seizes the opportunity to strike. The moment is both triumphant and bittersweet, as they realize the cost of their victory. The Mind Flayer is defeated, but the emotional toll is heavy.

In the aftermath, the group gathers outside the mall, their faces reflecting a mix of relief and sorrow. They have triumphed over the Mind Flayer, but the battle has left scars. Eleven, feeling the weight of her powers and the responsibility she carries, looks at her friends with a sense of gratitude and love. Mike, standing beside her, reassures her, their bond stronger than ever.

As the episode concludes, the camera pans out, capturing the group standing together, united yet changed by their experiences. The fate of each character is intertwined; they have faced darkness and emerged stronger, but the emotional ramifications of their battle linger. The scene fades, leaving the audience with a sense of hope tempered by the reality of their struggles.

In "Stranger Things 3," episode 4 titled "Chapter Four: The Sauna Test," there is no post-credit scene. The episode concludes without any additional scenes after the credits roll. The focus remains on the unfolding events in Hawkins, particularly the group's efforts to confront the Mind Flayer and the emotional dynamics among the characters. The absence of a post-credit scene allows the tension and stakes established in the episode to resonate without distraction.

The sauna test is a crucial experiment devised by the group to determine who among them is possessed by the Mind Flayer. They use the sauna's heat to induce a reaction in Billy, who they suspect is under the control of the Mind Flayer. The test is intense and emotionally charged, as it reveals the lengths the group is willing to go to protect their friends and confront the growing threat.

In this episode, Billy's character is explored more deeply as he struggles with the influence of the Mind Flayer. His internal conflict is palpable, showcasing moments of vulnerability amidst his aggressive behavior. The audience sees glimpses of his past and the pain he carries, which adds layers to his character and evokes a sense of sympathy despite his actions.

Eleven plays a pivotal role in the sauna test as she uses her psychic abilities to probe into Billy's mind. Her determination to save her friends and confront the Mind Flayer drives her actions. However, she also experiences emotional turmoil as she connects with Billy's pain, highlighting her empathy and the burden of her powers.

During the sauna test, the dynamics among the main characters shift significantly. Tensions rise as they confront the reality of the Mind Flayer's influence. Characters like Mike and Lucas show their protective instincts, while Max's loyalty to Billy complicates the group's decisions. This test not only strains their relationships but also solidifies their resolve to fight against the supernatural threat.

The outcome of the sauna test reveals that Billy is indeed possessed by the Mind Flayer, as he reacts violently to the heat. This revelation shocks the group and solidifies their understanding of the threat they face. The impact is profound, as it unites them in their mission to confront the Mind Flayer, but it also leaves them grappling with the emotional fallout of having to fight someone they once cared about.

"Stranger Things 3," episode 4 titled "Chapter Four: The Sauna Test," contains several elements that may be considered objectionable or upsetting for children or sensitive viewers. Here are some aspects to be aware of:

1. Violence and Threats: There are scenes that depict physical confrontations and threats, which may be intense for younger viewers.

2. Body Horror: The episode includes unsettling imagery related to the Mind Flayer and its influence on characters, which can be disturbing.

3. Emotional Distress: Characters experience fear, anxiety, and emotional turmoil, particularly in relation to the supernatural events occurring around them.

4. Mature Themes: The episode touches on themes of friendship, betrayal, and the struggle against a malevolent force, which may be heavy for younger audiences.

5. Language: There are instances of mild profanity that may not be suitable for all viewers.

These elements contribute to the overall tension and darker themes of the series, which may not be appropriate for all children or sensitive individuals.