In the near future, Earth is slowly dying because of all the damage humanity has caused and people are desperate to escape. One day a giant black sphere appears out of nowhere near Mars, so six astronauts are sent to investigate on a spaceship called Achilles. For eight months the crew spends the journey in hibernation.
Karla keeps dreaming about her daughter and her mother, who tragically died in a car crash two years ago. When there are only eight hours left to reach the sphere, the crew is woken up. While they take a moment to stretch their muscles and clear their heads, Karla notices that Rubin is rather rattled because this was his first time hibernating and she advises him to rest.
However Rubin prefers to blog his experience since he has a massive amount of followers. Afterward Karla meets with Commander Paul and they try learning more about the sphere by scanning it, but the ship's AI can’t find anything out there. Kara thinks they should go back, but Paul wants to finish their mission anyway.
The lack of data makes Rubin even more nervous than he already is. The crew decides to contact Vance, the head of the expedition program, who tells them people on Earth are eagerly waiting for an answer to the mystery. They can’t disappoint them, so the mission must be completed.
Sometime later Karla starts hearing her mother’s voice in the corridors but she doesn’t see anyone around. At the same time Rubin is startled awake by creepy whispers in his room. When Karla gets to her room, Vance video-calls her, saying he’s worried about her because she’s been looking tense.
As Karla assures him she’s fine, the call is suddenly cut off and the ship’s AI announces the sphere is causing an anomaly. Karla runs to the main deck and finds the mysterious sphere shooting a very bright beam of light at the ship, which is causing various issues in the system. The rest of the crew also runs to the deck and Tez points out the light seems to be a way to show the ship where to go.
As the ship continues to get closer, the AI picks up a noise coming from the sphere. When Karla analyzes it, they decode a message that repeatedly says “Deus”, which means God in Latin. Rubin panics and asks the crew to go back before he runs out of the room.
Karla thinks they should pause the trip and wait until the AI fixes the comms so they can inform Vance of this in case it’s a hostile alien, but Paul decides they’ll keep going. Afterward the crew checks on Rubin and finds him crying in the corridor. He’s still panicking and says the light is Judgement Day sent by God, which he knows because the voices told him so.
Rubin asks for the mission to be canceled again before he leaves. Then the crew discusses their theories and Ulph thinks it’s their duty to find out what the sphere is. If it turns out to be an alien trolling them, they can just blow it up.
Paul is following this on the cameras and calls Ulph to the deck to tell him not to mention blowing up things ever again. When the ship is about to reach the sphere, both Karla and Rubin start hearing the voices again. Ulph takes Karla to her room and she explains she’s been having headaches since the car crash, but she doesn’t mention the voices.
Their talk is interrupted by Tez, who informs them Rubin is missing. Ignoring Ulph’s concerns about his health, Karla joins the search. The team splits and Tez gets to check the cargo bay.
Hidden behind some containers, Rubin is surrounded by lights as he does a ritual to please the voices in his head. His skin is getting carved with a bunch of religious symbols. When Tez finally finds him, she screams in horror, so Karla and Ulph run to find her.
Unfortunately by the time Karla gets there it’s too late: Tez is dead on the floor with her guts out. Rubin notices Karla spying on him so he takes her hostage, threatening to kill her too when Ulph arrives. Sounding desperate, Rubin says they’re beyond redemption and if they land on the sphere they’ll be part of God’s slaughter.
He also claims that Paul is obviously hiding something so they should take the ship from him. At that moment Paul appears behind Rubin and shoots him without hesitation, instantly killing him. Then he tells Ulph to get two body bags, not showing any emotion regarding the loss of two crew members.
After grabbing Rubin’s knife, Karla follows Paul into the elevator and asks him if he really knows something. Paul denies it and gets angry as he senses she wants to quit the mission, but he reminds her that orders are orders. When they arrive at her room, Karla snaps and calls Paul out for behaving so coldly about their fellow team members’ deaths, but Paul just walks away.
Instead of body bags, Ulph decides to put the bodies in their corresponding hibernation chambers. With only three hours left before reaching the sphere, the crew separates the main Achilles frame and stays in a smaller ship to navigate through the sphere more easily. Karla notices some kind of structure on the sphere but can’t understand what it is.
When the ship finally lands on the sphere, the comms begin working again and the crew gets a call from Vance. He informs them that ten thousand unidentified structures like the one Karla saw have appeared on Earth but they don’t seem to be invading. Vance is convinced the sphere is behind this and wants the crew to solve the mystery as soon as possible.
Paul orders Ulph and Karla to go out to investigate, but Sean points out they’ll need a scientist and volunteers to go as well. The trio suits up and leaves the ship while Paul watches them on the cameras. The sphere is completely dark so they can’t see in the distance, and Karla’s scanner can’t pick up anything.
When she touches the ground, she says it isn’t an element known on Earth. Paul sends them to check the structure and by seeing up close they realize it’s a gate. Suddenly a bright light starts glowing inside the gate, so Ulph fires a flare to take a better look at the rest of the structure.
They see a symbol known as Event Horizon, which represents a boundary in which events can’t affect an observer. Karla calls it “the end of existence” and scans the gate, confirming it’s made from the same material as the sphere. At that moment the crew hears a weird noise, which shouldn’t be possible in a vacuum.
Paul tells them that the ship’s AI picked up a transmission and is sending it to them through their communicators. This transmission says “welcome”. When the light begins glowing brighter, a woman appears in the middle of the gate.
The woman is sending out messages with her mind and the AI translates them for the crew, revealing that this being claims to speak for the Creator of all existence. This Creator has come as a warning and to help by giving humanity a choice: those who enter the gate will find eternal peace, and Karla was the chosen one to show them the way. Inside the gate they’ll find the end of all suffering and pain, but those who choose not to enter will die when the sphere reaches Earth to destroy it.
Suddenly the woman turns into Karla’s mother and tells her that someone is waiting for her inside the gate. A shocked Karla walks into the light and has a flashback about the car crash before finding herself near a golden city with the accident wound still fresh on her head. Her daughter is there and Karla runs toward her, but before they can reunite Karla wakes up on a table in the ship.
After having a seizure, Karla throws up and wonders how she got there. Ulph explains she could barely stand when she came out of the gate, so he brought her back to the ship. Unfortunately Sean didn’t make it.
Their conversation is interrupted by a call from Vance, who wants to know all the details. Karla tells him about the golden city and compares it to Jerusalem, causing Ulph to call it “heaven”. She doesn’t mention her family even when Vance keeps asking questions, not believing her when she says she saw nothing else.
Once the call is over an irritated Paul leaves the room and Karla asks about Sean’s death. Ulph explains his suit ruptured and Karla doesn’t believe since their suits are made of a material that doesn’t break. Then Ulph says Sean didn’t secure his glove correctly and he decompressed but Karla doesn’t buy this either since Sean was a very experienced explorer.
A very suspicious Ulph reminds her that everyone makes mistakes and tells her to rest. Karla wants to explore the sphere again however Ulph informs her the ship is already leaving and follows her out. When they reach a corridor with no cameras, Ulph asks Karla what she really saw inside the gate so she tells him about her family.
She also explains she doesn’t trust Vance and Paul because it seems they’re hiding something. Moments later Ulph returns to the deck and Paul asks him what happened when he and Karla were out of the camera’s reach, but Ulph tells him Karla said nothing new. Paul gets suspicious and reminds Ulph to respect his orders.
Once the ship is out of the sphere’s orbit, the AI announces the crew should be ready to hibernate in one hour. After grabbing Rubin’s knife, Karla goes to the pods and checks Sean’s body, especially his suit. Next she breaks the lock to Paul’s room with the knife and goes inside to search for clues.
Paul sees her on the security cameras and sends Ulph after her. In Paul’s room, Karla finds a gun and some very interesting files. Soon Ulph appears outside the room and Karla stops him by pointing the gun at him.
Having read the files, now she knows he’s a former Elite Corps soldier and used to be known for being the best, however Ulph explains that was left in the past and swears he doesn’t know anything about the sphere. Karla forces Ulph to go back to the main deck, where she points the gun at Paul instead. He points out this is mutiny and the punishment is death, so Karla retaliates by revealing that Sean was killed by a gunshot.
She thinks Ulph did it since he used to be a hitman. The tense moment is interrupted by a call from Vance, who promises he isn’t her enemy and claims all his scientists believe she truly saw Heaven. He also plays a video showing people on Earth gathering on the streets, desperate to leave the planet after having seen the footage of the sphere Vance broadcasted.
Karla is left in shock and Paul uses the chance to jump on her. After some struggle, Karla manages to push him off and shoots him in the chest to kill him. Then she notices she got hurt during the fight and her stomach is bleeding.
After Vance hangs up, Karla points the gun at Ulph, who admits he did kill Sean. However he doesn’t want to kill her because he also wants to know the truth about the sphere and what she saw. Deciding to trust him, Karla lets Ulph take her to the infirmary and bandage her wound.
Once she’s feeling better Karla admits she wants to go back to the sphere but Vance controls the AI. Ulph reveals he has the code to override the AI, but they would have to drop the heel since the Achilles is too big to control manually. They’d lose the main propulsion and their trip back to Earth would take more than five years.
Karla is losing hope, yet Ulph has an alternate plan up his sleeve. Then Karla returns to the deck and calls Vance to tell him she’ll destroy the sphere if necessary, since she believes it’s a lie. Vance activates some classified files that show her the element she found on the planet, revealing he was the one who built the sphere.
There’s no God, he did all this to save six billion people and kill the remaining fifteen because Earth is overpopulated. There’s no God in the gate and the sphere can’t actually destroy Earth, it was all a lie to make people panic and cause them to run toward the gates that appeared all over the planet. They thought they were entering heaven but they were actually walking to their deaths.
Karla doesn’t understand how this could make her hear her family, so Vance admits he installed a chip in her head after the accident, which was also his fault. Everything has been part of his plan to train Karla for this trip. A crying Karla calls Vance a monster and shares a tale her mother used to tell her about how everyone deserves a chance to survive.
At that moment Ulph contacts her, announcing he’s got his hands on the Achilles’ core. Vance realizes the duo is planning to destroy the sphere and orders the AI to begin the ship’s auto-destruct sequence. Alarms start wailing and the AI announces that the Achilles will explode in three minutes.
Karla furiously shoots the hologram machine to end Vance’s call before contacting Ulph, who gives her the code to separate the main ship from the huge cargo structure. Ulph is still stuck in the elevator, which doesn’t move fast enough for him to return to the main ship in time. He tells Karla to leave without him and at first she refuses, but at that moment the self-destruction is triggered and the Achilles begins exploding at multiple spots at the same time.
Karla has no choice but to separate the ship and watches in horror how all the explosions destroy the main structure, thinking her friend is dead. However Ulph suddenly contacts her, revealing he crossed over at the last second. Afterward the duo celebrates their survival with a drink and Ulph explains that since they lost half of the Achilles, the detonation of the core will have to be done manually.
Karla accepts this and says they’ll do it together. However when the ship lands on the sphere, Ulph closes the door behind him and tells Karla to go back to Earth so she can tell everyone the truth. Karla leaves on the ship and shares a final goodbye with Ulph, who waits until the ship is far enough to detonate the core and destroy the sphere at last.
Karla is now traveling alone to Earth and the AI informs her that the trip will take seven years.
