The film begins in the bustling streets of New York, where an unsettling event unfolds in Central Park. People become disoriented, repeating their words, standing frozen, or even moving in reverse, creating a chilling atmosphere marked by sudden screams. During this chaos, a woman named Alison Folland takes a drastic action, using her hairpin to tragically stab herself in the neck. At a nearby construction site, a group of workers, including Curtis McClarin and Michael Den Dekker, are startled when a worker falls to his death from the roof. They rush to the scene, but soon they witness more of their colleagues succumbing to this inexplicable fate, seemingly compelled to plunge to their demise in a calm and fatalistic manner.
In the classroom, we meet Elliot Moore, portrayed by Mark Wahlberg, a science teacher who grapples with an inexplicable phenomenon—the mysterious disappearance of bees. When a student speculates on the nature of this event, Elliot is unexpectedly called away to a staff meeting. There, he learns about ominous reports of a potential "terrorist attack" involving a toxic gas released in the city, prompting authorities to cancel school. As he confides in his friend, John Leguizamo's character Julian, Elliot reveals the strain he and his wife, Alma played by Zooey Deschanel, are experiencing in their marriage.
As panic spreads, Elliot, Alma, Julian, and his daughter Jess (played by Ashlyn Sanchez) flee Philadelphia by train. Yet, as they receive dire reports on their phones about the escalating chaos, Alma receives persistent calls from a mysterious person named Joey (voiced by M. Night Shyamalan), which she hides from Elliot.
The setting shifts to Rittenhouse Park, where a traffic cop (played by Don Castro) casually discusses the weather until a sudden, violent chain reaction begins. Following a gunshot, he falls, and soon after, a taxi driver named Sal (portrayed by Bill Chemerka) takes his own life using the cop’s gun. The sense of dread intensifies as a woman steps into the chaos and pulls the trigger once more.
The train unexpectedly halts in a sparsely populated rural area where they discover on a diner TV that the tragic suicides are potentially linked to a natural toxin. A scientist explains how this toxin disrupts the brain's self-preservation instincts, instigating a growing fear. Julian, desperate to reach his wife, sets off to Princeton, unaware of the horrors awaiting him, while Elliot, Alma, and Jess decide to head for safety away from the chaotic northeast.
As they venture deeper into the wilderness, they encounter a couple running a plant nursery who theorize that the source of this chaos could lie in plant communication—a compelling idea that offers a glimpse into the possible natural origins of their plight. After a series of chilling encounters, including witnessing mass violence and self-harm, the group splits to evade the sinister force of the toxin.
Alma, feeling a need for honesty as they navigate the terror, confesses a moment of temptation with Joey, while Elliot, acknowledging his own distractions, tries to maintain a facade of normalcy. Their journey is filled with surreal moments, including Elliot's humorous interaction with a plastic plant, showcasing the thin veneer of sanity juxtaposed against a backdrop of increasing madness.
Their desperate attempts to find shelter lead them to an old house, where a reclusive lady offers temporary refuge. Time passes, and an ominous newscast hints at the peak of the violence set for the following morning. As the toxin continues spreading, the trio finds themselves in a race against time, discovering that even solitude is no sanctuary from this new threat.
In a climactic moment, they decide to unite, holding hands amidst an eerie stillness, only for the calm to prevail as the horror seemingly passes.
Three months later, life in Philadelphia returns to an eerie normality. Jess heads off to school, and as Alma discovers she is pregnant, the couple shares a moment of hope amidst the lingering dread of the past. Meanwhile, a scientist warns on TV that humanity might be facing a dire reckoning as nature reacts against its perceived intruders. In a haunting final shot, the tranquillity of Jardins du Louvre in Paris is shattered by a distant scream, suggesting that the darkness may not be entirely gone.
