Plot summary

Before the movie starts, an off-screen news broadcast informs the viewer that the situation on Earth is quickly deteriorating due to an imminent energy crisis which is causing several countries to threaten war. The film opens with Hamilton (Gugu Mbatha-Raw), a British scientist, waiting in a car with her husband, Michael (Roger Davies). They are stuck in a traffic jam and discuss the frequent blackouts happening around them due to the energy crisis. We learn that Hamilton received an invitation to take part in a mission aboard the space station Cloverfield in order to test the Shepard particle accelerator, which will provide the Earth with infinite energy if operational. As the title sequence appears, the film now takes place on station two years into the mission, as the crew is testing the Shepard for the umpteenth time. The crew consists of Hamilton; Schmidt (Daniel Brühl), a German scientist working on the Shepard; Tam (Ziyi Zhang), a Chinese scientist also working on the Shepard; Volkov (Aksel Hennie), a Russian scientist in charge of life support and ensuring that the ship's electronics are properly functioning; Monk (John Ortiz), a Brazilian and the crew doctor; Mundy (Chris O'Dowd), an Irish technician; and Kiel (David Oyelowo), the American crew commander. The test fails, with the particle accelerator failing to output more energy than is being input into it.Hamilton is seen talking over a webcam-like communication to her husband on Earth, informing him that the test failed and that they only have enough fuel for three more tests. On board the ship, tensions between the crew grow, with Volkov accusing Schmidt of taking his time with the tests while the former's mother country of Russia is nearing desperately low levels of energy and is threatening war on the Western world. Schmidt denies these allegations, while Kiel attempts to defuse the situation. The crew gears up for yet another test, while Monk watches a news report on Earth. In said news report, a man named Mark Stambler (Donal Logue) is being interviewed, who warns that if the Shepard becomes operational, it may open an inter-dimensional gateway that could lead "monsters, demons, and beasts from the sea" to enter the current dimension, but also other dimensions and past and future timelines. The crew dismisses it as nonsense and begins the test. This time, it appears that the particle accelerator works; however, it quickly overloads, creating an energy output far above normal levels. It catches fire, and the condensation system used to cool it down fails to work, leading Tam to suggest ventilating the system instead. Upon fixing this, the crew discovers to their horror that they are no longer orbiting the Earth. They originally assume that they may have destroyed the planet accidentally when testing the Shepard, but later come to the conclusion that they have been warped to an entirely different part of the galaxy.The crew discovers that the gyro (a navigational object that allows the ship to get its bearings) has inexplicably gone missing, as they begin hearing horrifying screams coming from the walls. After opening the wall panel where the screams originate, they discover to their great shock a young woman (Elizabeth Debicki) inside it, fused with electrical wires. They are able to rescue her and use an advanced medical bay to restore her body to a healthy condition, but are taken aback by the fact that she seems to know Hamilton. Back on Earth, Michael awakens to a gigantic explosion. He checks his phone and sees conflicting reports assuming the Russians attacked the city, then discovers "something else" was the cause. He decides to head down to the hospital where he works to help the presumed victims.Meanwhile, Volkov begins to feel something crawling underneath his skin, and discovers that his eyes are moving out of orbit on their own. After facing the mirror and seemingly talking to himself, he overrides the security controls of an on board 3D printer to craft a handgun and ammunition. He then confronts Schmidt on X-Deck (the area where the Shepard can be repaired from) and points his gun at him and Tam, accusing the German of working for his country's spy agency. He suddenly collapses on the ground and is taken to the ship's bridge, where he begins convulsing and suddenly has worms that had previously gone missing from the ship's laboratory explode from inside his body, killing him. Speaking to the young woman in the medical bay, Hamilton discovers that her name is Jensen, and that she claims to be a crew member of the Cloverfield and to know all of the members on the ship except for Tam. She then warns Hamilton that Schmidt is not to be trusted. Upon an off-screen investigation, Kiel discovers that the German is indeed working for the German government and is tasked with purposely sabotaging the Shepard in an effort to cause Russia to collapse due to the energy crisis. Schmidt vehemently denies this, but Kiel locks him into a containment area until further notice.Michael is talking on the phone to a contact at the space agency, who tells him they lost contact with the station his wife is on. Something catches his attention, and he stops the car in front of a destroyed building. Through the smoke, a gigantic shadowy figure is briefly seen, which then disappears as a child (Clover Nee) is heard crying for help. Michael goes to help her.As Mundy is repairing the wall panel they opened earlier, his arm is suddenly sucked into the wall panel. Kiel and Hamilton arrive to pull him out, and soon discover that his arm is no longer attached to his body. Monk remarks that it looks like he was born without an arm, rather than it being violently severed from his body. Meanwhile, Schmidt is let out of the containment area by an unknown presence. To his bewilderment, he discovers Mundy's arm crawling around the ship on its own. The rest of the crew arrives and captures it, and discover that the arm is attempting to tell them something. After the crew gives it a pen, the arm compels them in writing to open Volkov's body. They do so, discovering the missing gyro inside the Russian's body. After fitting the gyro back into its slot, they discover that they are still in the Solar System, yet the Earth is on the opposite side of the Sun. They re-establish communications with the planet and discover through broadcast news that there has been a global war over energy raging for the last fourteen months, and that the Cloverfield station was destroyed long ago. They arrive at the conclusion that the Shepard opened a gateway to another dimension, which they traveled to and which caused all of the anomalies on the ship to happen. They are now so far away from the Earth because while their location did not change, the Earth's orbit caused it to move to a different point on its path fourteen months into the future. The dimension they find themselves in is not their dimension, but it's Jensen's dimension, as well as presumably the dimension of Mundy's arm. This also explains how Jensen knows the crew, why she doesn't know Tam (she has the same role as Tam on the station and therefore was the crew member who replaced her in her dimension), and why they believe Schmidt to be a spy (his counterpart in Jensen's dimension was indeed working for the German government).They theorize that by recreating the last test with the Shepard, they will be able to return to their own dimension. Back on Earth, Michael and the child, whose name is Molly, drive to a friend's shelter in order to stay safe during the mysterious ongoing conflict in the city. On the ship, Tam discovers that the Shepard failed because condensation caused by the cooling system threw off the data she received at the end of each test. Ventilation, on the other hand, would have created the necessary conditions for a stable beam. She goes into one of the airlocks to attempt testing such a theory, but she finds herself locked inside it as water pours out of the condensation system, filling the room. The other crew members attempt to free her but are forced to watch in horror as the water creates pressure on the outer door of the air lock and breaks it open, causing the water to freeze instantly and killing Tam. In order to get the Shepard up and running, Kiel decides to entrust Jensen in taking Tam's place on X-Deck, since the two shared the same role in their respective dimensions' crews.In the shelter, Michael is on the phone with his contact at the space agency when loud noises and heavy shaking cause him and Molly to panic and the power to go off. Jensen informs Hamilton that her children, who died in the latter's dimension after she installed a power core in their home that failed and caused the house to burn down, are alive and well in Jensen's dimension. This leads her to deciding to stay in this dimension. She informs Kiel of this decision, who is reluctant at first but comes to accept it. The crew realize that they need to reroute power from other systems to the Shepard to provide the necessary yield, and decide to shut down the life support, leaving a mere two hours of oxygen for the crew. Mundy undertakes the task of doing so in a small storage room and succeeds, but a magnetic disturbance causes his tools and a gas canister to fly towards the wall, causing an explosion that kills him and destroys a part of the ship. Kiel, Hamilton, and Monk are forced to go into the damaged part of the ship and jettison it into space in order to save the remainder of it. Upon arriving there, Kiel realizes that he needs to close the air lock behind him to do so, and sacrifices himself to save the rest of his crew. On Earth, Michael records a message on his phone to Hamilton, telling her that the only thing they can do is save the people that they still can.On the station, the remainder of the crew hastens to put their plan to fruition, with Hamilton informing Schmidt and Monk of her decision to stay in the alternate dimension. Jensen secretly takes the handgun that Volkov had and brings it with her and Hamilton to the escape shuttle, where she knocks Hamilton unconscious with it and proceeds to return to X-Deck. Hamilton regains consciousness in time to hear Jensen shoot Monk, finding him dying when she follows the sound. She then arrives to X-Deck to see Jensen pointing the gun at an injured Schmidt's head. Jensen informs Hamilton of her decision to keep the Cloverfield station in her dimension because it would save the people of her planet, rationalizing that she would gladly kill three people to save eight billion. Schmidt uses a nearby metal rod to knock her to the ground, allowing Hamilton the opportunity to escape. In the ensuing struggle, Schmidt is shot in the shoulder. Jensen hunts Hamilton through the ship, who takes her by surprise and attempts to wrestle the gun from her. Unable to secure the gun for herself, Hamilton decides to fire three rounds into a nearby window, opening the room to the vacuum of space and causing Jensen to be sucked out, killing her.Instead of staying in the alternate dimension, Hamilton decides to record an audio message warning her counterpart of the dangerous power cell inside the house, and attaches the data for the Shepard to function properly to the message. Then, she and Schmidt overload the Shepard again, allowing them to return to their dimension. They make radio contact with Earth and successfully establish a stable beam for the Shepard, completing their original mission. They inform the Earth of this, and prepare to jettison down to the surface now that an infinite energy source has been created. Meanwhile, Michael's agency contact informs him of their success, and tells him that they are returning to the surface. Michael angrily responds that they should not have been allowed to return to the Earth while "these things" were roaming the surface. The last shot shows the shuttle crossing the cloud barrier, immediately followed by a gigantic monster very similar to the creature that destroyed New York City in Cloverfield (2008), albeit far larger, breaking through the clouds and letting out a terrifying roar.