The Hess family resides on a quaint farm in Doylestown, Bucks County, Pennsylvania. At the center is Graham Hess (Mel Gibson), a former Episcopal priest whose faith was shattered following the tragic loss of his wife, Colleen. She died in a tragic traffic accident caused by veterinarian Ray Reddy (portrayed by M. Night Shyamalan), leaving Graham grappling with his grief and the burden of his son Morgan's (Rory Culkin) asthma condition, which greatly troubles them. Graham’s life, devoid of religious practice, includes his daughter Bo (Abigail Breslin), known for her odd habit of leaving half-finished glasses of water, and his younger brother Merrill (Joaquin Phoenix), a former minor league baseball player whose inability to make it to the majors haunts him.
Graham's mundane existence takes a turn when a mysterious crop circle appears in their cornfield, stirring speculation among the townspeople about its origins. While some dismiss it as a prank, others suspect it may be the work of intelligent extraterrestrial beings. Events escalate when unsettling reports of aggravated animal behavior emerge, culminating in a harrowing moment when Morgan is forced to kill their dog after it attacks Bo. The incident leaves him traumatized and silent.
As the plot unfolds, the Hess family realizes they are being watched. One night, Graham and Merrill pursue a shadowy figure lurking on their barn roof, which vanishes into the fields. Soon, they discover that similar crop circles have appeared globally at an alarming rate. Morgan becomes fascinated with a sheriff's radio walkie-talkie, only to learn that he can communicate through a baby monitor, which they find at home. When strange, bubbling noises emanate from it, he climbs onto the car roof for better reception, rallying his family to form a human chain in an attempt to amplify the signal – a notion he believes may attract the mysterious visitors.
During one particularly tense night, Graham investigates the source of their other dog's barking, only to encounter strange clicking sounds in the corn. Firmly, he warns the unknown being that their family won't be toyed with. What follows is a shocking glimpse of a long green leg slipping into the cornstalks. This moment spurs him to allow his family to turn on the television, revealing that large mysterious lights are now being sighted over Mexico City.
In a profound moment of introspection, Graham discusses his lost faith with Merrill, who recounts moments that make him believe in miracles. Graham's moment of reflection is punctuated with a harrowing flashback of the accident that claimed Colleen’s life, revealing the emotional depths they now face.
The next day brings astonishing news footage of an alien sighting during a boy’s birthday celebration in Brazil. After visiting Ray Reddy, Graham receives ominous warnings about the aliens’ aversion to water and hints at having trapped one in his pantry. Attempting to confront the intruder, Graham gets more than he bargained for, leading to panic as he stumbles upon an alien hand trying to claw its way to him.
Determined to protect his family, Graham proposes they either flee to the lake or fortify their home. After a family vote (with Graham joking that he votes for two, in honor of Colleen), they fortify their home with boards against the imminent threat. As they prepare for the worst, they share a final dinner that stirs up poignant memories of their lost loved one. In a heartwarming scene, the family embraces, crying together at the realization of the depths of their grief.
Their serenity is shattered when the baby monitor emits familiar noises, prompting them to seek shelter in the basement. As they instinctively hide, the tension mounts when something lurks above, signaling the start of a struggle for survival. An alien suddenly grabs Morgan, injecting him with a toxic gas, heightening the family’s desperation.
Graham’s memories of his wife's final moments echo back to him: her love, her pleas for him to watch over their children, and her strange encouragement to "swing away," tied to Merrill's passion for baseball. With renewed determination, Graham instructs Merrill to act on Colleen’s words. Merril seizes his old baseball bat, unleashing his pent-up skills on the alien, while Graham rushes to save Morgan from the invasion outside.
In an extraordinary twist, they discover that the alien is vulnerable to water, harnessing the unfinished glasses left by Bo to defeat it. With Morgan’s life saved, Graham’s lost faith rekindles, ultimately leading him back to his clerical roots as the chilling winter weather blankets the land outside. The film beautifully culminates with Graham donning his clerical suit once more, signaling a triumphant return to faith and family.
