Linguist Louise Banks (Amy Adams) is deeply affected by the loss of her young daughter to cancer. As she continues to lecture at a university, twelve extraterrestrial craft suddenly make their appearance on Earth. In a twist of fate, Colonel Weber (Forest Whitaker) from the U.S. Army recruits Louise to collaborate with Ian Donnelly (Jeremy Renner), a brilliant experimental physicist, to decode the aliens' language and determine their purpose for visiting.
Assigned to a military base in Montana, near one of the spacecraft, the team gains access to the mothership where two astonishing seven-limbed aliens, dubbed the "Heptapods," await. They affectionately name the extraterrestrials "Abbott" and "Costello." Louise begins her arduous journey of understanding their complex written language, which consists of intricate circular symbols. As her skills improve, she begins to experience vivid and surreal visions of a girl she doesn’t recognize as her daughter.
In a pivotal moment, when she asks the aliens what they desire, they respond with the cryptic message: > "offer weapon." This alarming translation sparks fear among world leaders, leading some countries to sever communication and prepare for military aggression against the Heptapods. Yet, Louise starts to suspect that the intended meaning behind "weapon" could potentially signify "tool" or "technology," hinting at a more benevolent purpose.
Amidst growing tensions, rogue military personnel place explosives inside the spacecraft unbeknownst to Louise and Ian. Upon their re-entry, the aliens reveal a far more intricate and significant message. Just as an explosion rocks the ship, Abbott ejects them, rendering them unconscious. Upon awakening at the military base, Ian realizes that the circular symbols are connected to a non-linear perception of time, suggesting that the aliens are urging human collaboration for a larger cause.
With time running out, Louise learns that China is preparing a military strike against the spacecraft. In a race against time, she returns to the craft where she encounters Costello, who discloses that Abbott’s life is waning. Louise’s visions of the daughter she hasn’t yet had are actually glimpses of her future. Costello reveals that they have come to aid humanity by sharing their language, which serves as a "tool" to alter our perception of time. The Heptapods anticipate a future event when they will need humanity's help, pushing Louise to use her newfound insights.
As the situation escalates, Louise experiences a vision of a future United Nations event where she is thanked by General Shang (Tzi Ma) for convincing him to hold off on the impending attack. In a key moment, he shares that she called his private mobile phone, recalling a number he doesn’t fully understand. In a powerful act of faith, Louise takes a satellite phone and attempts to reach General Shang, despite feeling unprepared for what she must say.
Her vision reveals that she successfully persuades him by mirroring his wife's last words in Mandarin, leading to a halt in the military offensive and restoring dialogue between nations as the spacecraft vanish from the skies. As tensions ease, while preparing to leave the military camp, Ian boldly confesses his love for Louise. They reflect on choices in life and whether knowing the future would alter their decisions. Louise envisions Ian fathering their daughter, Hannah, whose name is deliberately a palindrome, yet realizes he will leave her after learning their daughter’s tragic fate. Despite knowing the heart-wrenching road ahead, when Ian asks if she’d want to have a child, Louise embraces the future with hope.
