As a child, Ellie has always been curious about astronomy and radio signals. She can spend the whole afternoon at the radio contacting different parts of the world just for fun, keeping track of all her calls on a map. Her father always supports her and they often look at space together with a telescope.
Ellie dreams of contacting aliens some day, but sometimes she also wonders if she could also use a radio to communicate with her dead mother. Years later, Ellie is a doctor working for the Search for Extra-terrestrial Intelligence program or SETI at the Arecibo Observatory in Puerto Rico. Just like during her childhood, she spends hours sitting at a radio searching for emissions sent by aliens to prove they’re real.
Her blind coworker Kent has respect for what she does because nobody sits to just listen anymore. Ellie starts a new map marking all the spots in the galaxy she’s already checked. One day while having lunch at a restaurant, Ellie is approached by Palmer who asks about the observatory’s current work.
He’s writing a book about how technology affects Third World countries and has a little plastic compass that he tries to gift Ellie, but she gives it back. Palmer gets flirty and they agree to meet on Tuesday. Soon the President's science advisor David arrives to check on the research but it’s clear he doesn’t want to be there.
On Tuesday night they throw a party and David keeps explaining how science projects need to make profit since it’s using people’s taxes. Ellie tries to explain the importance of scientific research and Palmer comes to her defense, only for David to call him “father”. As Ellie’s mood drops, she asks Palmer if he’s a priest and he denies it, explaining he got a Master in Dininity and now he does secular humanitarian work with the support of Third World churches.
Ellie is skeptical but she still leaves with him and they watch the stars for a while so she can share some of the things she knows. She also tells him the story of how her dad inspired him to become an astronomer. The duo shares a kiss and ends up spending the night together.
After they’re done, they have a philosophical talk about God and science. Palmer truly believes in God but Ellie thinks there must be an explanation for everything. Then Palmer asks Ellie about her childhood, learning her mother died during childbirth and her father when she was nine.
Ellie gets uncomfortable and announces she must go to work, but she tells Palmer to leave his phone number. On her way out, Ellie remembers the day her father died. That night she heard a noise and went downstairs to discover the dad collapsed.
She had to run back and get the medicine from the upstairs bathroom, but it was too late. Later during the funeral, a priest explained to her that it had been God’s will but Ellie disagreed. She thought she just should’ve kept medicine in the downstairs bathroom too.
Afterward she ignored the other people and rushed to her radio to see if she could contact her father. In the present, Kent informs Ellie that David has shut down their project. A furious Ellie rushes to yell at David, who believes she’s wasting her time so he’s saving her career.
Then Ellie returns home and finds Palmer’s number with the little compass. However she calls Kent instead and announces she’ll search for investors so their group can continue their research in New Mexico. When she moves out, she leaves Palmer’s number behind.
Thirteen months later after many failed meetings in other companies, Ellie arrives at Hadden Industries to make her case, but the board calls her ideas “science fiction”. Ellie snaps and rants, pointing out all science discoveries were science fiction at some point in history. At that moment the board gets a call from CEO Hadden himself, who agrees to fund her research.
Four years later, Ellie’s is still in New Mexico working with massive satellite dishes. One afternoon Kent comes with bad news, saying they’re getting pressure from the scientific community to present results. Hadden is willing to fund the project for years, however the telescopes are government-owned and they want to lease them to more profitable people.
It’s been decided that the project will be shut down in three months. Ellie wants to fight however Kent thinks it’s time to admit defeat. In the meantime, Palmer has published his book and has become a spiritual counselor at the White House.
He appears on TV and explains he isn’t anti-technology, but he believes people have lost the way because they’re obsessed with computers instead of finding meaning in life. Days pass and Ellie never stops listening. One evening, she’s shocked to hear a pulsing noise.
Getting very excited, she immediately calls her team to give them the coordinates while she rushes back to the observatory. The team gets excited too and starts connecting as many machines as possible as they turn the satellites to get a better signal. They work together to do all the tracking and recording, happily confirming it comes from outer space.
It appears to come from the star Vega, twenty-six light years away. This means it’s been travelling for over twenty years. Suddenly the transmission stops and Ellie is about to lose hope, but luckily it soon restarts.
Ellie realizes the pulses represent prime numbers, which means it’s not random and someone specifically sent it. After the team argues on how to proceed, they agree to call everyone. The next morning the area fills with reporters and national security advisors.
The team explains other stations have confirmed their discovery, but National Security Council leader Kitz is still not happy that the team told the world instead of keeping the information classified. At least this time David defends her, explaining that without the help of other stations they would’ve lost the signal. With Kent’s assistance, they discover a second signal coming with the first one and they connect it to a TV.
The team starts messing around with the settings and finally manages to decode the signals into a video message: it’s a recording of Hitler's opening speech at the Olympics. This is the first television transmission that went into space and the aliens have sent it back as a hello. The White House panics and the president makes an announcement of the alien contact while trying not to mention Hitler, assuring reporters that the message is benign.
Ellie gets ready to talk in public, however David is called as the leader of the investigation instead. Meanwhile Kent continues to analyze the signal and realizes it has structure. They put together all the extra frames that don’t belong to the Olympics video and discover it translates into massive amounts of data.
Soon Ellie makes a presentation about this data and David announces the government will take over the decryption, causing Ellie to protest because this has always been her private work. White House official Rachel allows Ellie to keep control of the investigation but all progress must always be privately discussed with the government first before making any public announcements. Soon media all over the world is talking about this discovery.
Neo-Nazi protesters take over the streets while religious attendance is on the raise. Health organizations are also worried that mass self-deletion may become a big problem because some cults have already started to die. As everyone on TV starts arguing science versus religion, thousands of people camp outside the facility in New Mexico.
Some are just praying, others are just watching, but many are also protesting. Ellie is shocked to see a shady organization is offering UFO abduction insurance. At least most people are having fun, but she worries about a religious fanatic named Joseph who keeps inspiring hate.
Three weeks after the discovery, Ellie goes home to find an e-mail from an unknown sender. The text says “take me to your leader” and Ellie replies “who are you”. The answer quickly comes saying “I’ve got a secret” and showing part of the alien message.
As Ellie gets angry over a potential hacker, she gets a phone call and fax for a special appointment. Moments later a helicopter drops Ellie at the airport and she enters a private plane to meet Hadden, the man who funded her research and sent those e-mails. He lives in that plane and considers Ellie one of his most valuable investments, which is why he researched her.
Hadden plays a video that summarizes Ellie’s life and achievements before revealing he used to be an engineer too, which is why he hates how the government and religion get in the way of science. Then Hadden announces he’s deciphered the data and plays it on the screen, showing it must be arranged in three dimensions to understand it. The next day Ellie presents this discovery to the government, explaining the data contains blueprints for some kind of machine.
Since they can’t tell what the machine is for, an argument ensues to decide if building it or not, since it could be dangerous. The subject of god keeps coming up and Ellie is shocked to see Palmer arrive, saying they should find a middle point. The argument is interrupted by the arrival of the president, who hears everyone out.
That night a party is thrown to celebrate this progress and many protesters gather outside, including Joseph. They ask scientists to get a real job instead of wasting tax dollars. Ellie meets with Palmer and they have another philosophical discussion.
She explains she needs proof of things and Palmer asks her to prove she loved her father, which leaves her speechless. At that moment they’re interrupted by big news that leaked on TV: it’s been discovered that the machine is a one-person spacecraft. An emergency meeting is held at the White House and they agree to build the machine, so the president will contact other nations to spread the risk and cost.
A selection committee is formed and Palmer is in it, they’ll interview a bunch of candidates to decide who gets to travel in the machine. To Ellie’s shock, David resigns as science advisor so he can be a candidate too. Soon media starts discussing how much this whole project will cost the country and who is worth of making such a trip.
There’s a lot of controversy surrounding the ten final candidates because one-third are American and Japan doesn’t volunteer anyone in exchange for a systems integration subcontract. Ellie appears on TV saying the traveler should understand the language of the message and that she doesn’t think the aliens would send them something that doesn’t work, so it shouldn’t be dangerous. This doesn’t stop the top astronaut on the list from withdrawing his candidacy when his scared children ask him to.
Later Ellie meets with Palmer and explains that due to time dilation, the person will only spend four years in the ship but fifty years will have passed on Earth. She thinks the sacrifice is worth it if it means finding such important answers, and they end up kissing again. On the day of the candidate interviews, Ellie does incredibly well and the committee is ready to finish.
However Palmer cuts in to ask her about her atheism, which makes her look bad in front of everyone. In the end, David is the chosen one. In the evening, Palmer visits Ellie to explain he couldn’t choose someone who thinks most of the world is delusional, so a crying Ellie gives him back the compass and kicks him out.
The machine is built at the Kennedy Space Center in Cape Canaveral, and crowds begin gathering there too. Lots of testing is being done using a robot to detect any side effects for the passenger. On the day of the launch, Ellie attends the event and David tells her he wishes her idealism had been enough, but unfortunately the world runs on a profit system.
Then Ellie joins the team in the control room and watches in excitement how the spacecraft is activated, its rings rotating around it as some sort of accelerator. While the final tests are run, Ellie looks at the monitor and notices Jospeh pretending to be a worker near the ship. She immediately warns David and everyone runs to tackle Joseph down, but it’s too late: he activates a bomb and a huge explosion brings down the tower.
As the crowd panics and runs, the falling parts destroy the ship and kill a bunch of workers, including David. Some debris flies off but nobody gets hurt outside the ship area. Sometime later, the authorities hold a proper funeral for the fallen ones while the news show the goodbye video left by Joseph, in which he said he did everything for the goodness of mankind.
When Ellie returns home, she discovers some machines waiting for her in her room. She presses a key and a videocall starts, revealing Hadden in the Mir space station. He’s living there because he’s dying of cancer and wants to have his last days in space.
He zooms in on a camera in Hokkaido Island, surprising Ellie with a second ship built by Japan. The company that got the contract is a subsidiary of Hadden’s and did all this in secret. Ellie immediately travels to Japan in Hadden’s private plane and meets the team in a big ship.
They teach her all she needs to know about the trip and share the safety precautions, including a container of poison. They’ve given this to astronauts for years in case they need to self-delete because they could get stuck floating in space after a ship failure. In the evening, Palmer visits Ellie and gives her the compass, confessing he actually didn’t vote for her because he didn’t want to lose her.
Soon the media is announcing there’s a second machine, but no reporters are allowed on the site. On launch day, Ellie gets nervous when she sees all the rings rotating but she advances anyway. The technicians make all the connections to her suit and put a camera on her head so the whole trip gets recorded.
Palmer uses his contacts to bring Kent in so he can give Ellie a good luck message before take-off. The ship begins vibrating which is normal, but Ellie also notices a strange light. She tries recording it for the team, but the footage is all static.
She theorizes it must be some electromagnetic field and is shocked to see the ship becoming transparent. The countdown begins and the team is worried, especially when the ship starts glowing and all the numbers on the computers are off-limits. They consider aborting the mission, however Kent hears Ellie’s voice through the static swearing she’s good to go.
The sea starts going crazy in the area and shakes the ship right before the spacecraft finally takes off. Ellie is amazed by the lights that surround her, which quickly turn into the most amazing and beautiful celestial views. This soon turns into a tunnel and Ellie theorizes it’s a wormhole, describing the whole experience for the camera even though she can’t communicate with ground control anymore.
After crossing what appears to be residual radiation, the ship stops and Ellie sees Vega. Looking around reveals a weird contraption nearby, only for the ship to suddenly take off again. Now Ellie flies through a series of wormholes, which keeps having a strange effect on her face.
Eventually it stops at another star system and Ellie notices a city on a planet. She barely gets to see anything else before the ship enters a much more violent wormhole and the compass starts floating, so Ellie leaves the chair to catch it. At that moment the chair beaks off and hits the ceiling before the lights go out.
Ellie turns on her flashlight and discovers a celestial event she can’t identify. She’s incredibly moved by its beauty and says a poet should’ve been sent to describe it. Suddenly she finds herself floating down and she appears on a beach.
This place is also beautiful and looks like a drawing she made as a child. Poking around causes her hands to meet resistance, meaning this so some kind of energy or illusion. At that moment a figure starts running toward her and Ellie is shocked to see her father, but as soon as she hugs him she realizes he isn’t real.
This is an alien, who explains he took this form to communicate with her more easily. He confirms there are many alien races out there and that humans contacted the universe first with their radio transmissions. The travel system Ellie used wasn’t built by his people, it was made by an unknown entity.
The aliens watched humans and agreed they were worthy, so they sent them the blueprints as a first step for humanity to join the rest of the universe. After he says goodbye, Ellie watches a beautiful meteor shower appear in the sky. A light suddenly shines too brightly and Ellie finds herself back in the ship, which is landing back in the Japanese sea.
The team panics and contacts Ellie, saying there was a malfunction and the ship never left. After Ellie is rescued she shares her whole experience, but the camera only recorded static. She swears it’s all true, however Kitz shows her a recording of the ship falling in seconds.
The next day the president gives a speech saying this is only a misstep, but soon the other nations are getting into legal disputes. The media is full of criticism and conspiracy theories, especially when Kitz steps down from his advisor position. Afterward a Congressional Committee led by Kitz interrogates Ellie, who points out a wormhole can explain what happened.
Time dilation could've made one second on Earth equal eighteen hours out in space. Kitz immediately calls her out because wormholes are just a theory and drops a big bomb: Hadden has died and it’s believed this whole deal had been a hoax organized by him. Ellie cries as she begs people to believe her story, shocking herself by requesting them to have faith since she has no evidence.
Her speech about awe, humility, and hope, inspires Palmer but the committee concludes her story is also a hoax. On her way out, Palmer joins Ellie in front of the cameras and a huge crowd, telling the world he believes her. Meanwhile in secret Rachel tells Kitz that Ellie’s camera recorded eighteen hours of static.
Eighteen months later, Ellie is working at a new base with extra radars since now SETI has enough funding to keep going. Kids visit the base during school trips and Ellie teaches them they must seek their own answers.
