Catering business owner Julia and her assistant Paul find themselves on a treacherous journey to an isolated mansion in New York to cater a small gathering hosted by Mrs. Perch and her son Sydney, as they honor their deceased patriarch. Among the guests is the town's mayor, Caruthers. However, the event takes a horrifying turn when mutated and deadly wasps launch a terrifying attack on the attendees, resulting in chaos and fatalities. Soon, Paul and Julia discover that these monstrous wasps reproduce by stinging humans, leading to the gruesome birth of giant wasps that kill their hosts.
Only a handful of them, including Paul, Julia, Caruthers, Sydney, and cook Flora, manage to flee into the safety of the house. As the outside world falls silent due to the phone lines being cut off by a car crash, the survivors realize their only hope lies in hiding out in the basement. In a shocking turn of events, Mrs. Perch is stung, leading to a grotesque transformation as a giant wasp births from her, claiming her life. Flora meets a similar fate, leaving Paul, Julia, Caruthers, and Sydney to navigate their escape.
With their only means of escape, the catering van, situated outside and with Paul’s keys left behind, tension rises as he bravely ventures out to retrieve them, battling a wasp in the process. Unfortunately, the danger intensifies when it is revealed that Sydney has also been stung, resulting in him becoming a pawn under the wasp's control before being subdued by Paul and Julia. As they strategize to escape the house, the ever-present threat looms large; tragedy strikes when Caruthers is fatally attacked by a wasp, leaving Paul and Julia desperately seeking an exit.
In a heart-stopping moment, they escape to the outside, yet the nightmare continues as Paul is snatched away by a wasp, bringing him to a nest commanded by the monstrous offspring of Mrs. Perch. Just as the situation seems most dire, Julia’s timely arrival leads to a fierce showdown where she rescues Paul and detonates the nest, taking a hard stand against the relentless wasps.
As they flee in their car, a flaming wasp pursues them, prompting Paul to ram the vehicle into a tree in a desperate bid to eliminate the threat. Julia initially resists abandoning the fight, leading them to crash the car, ultimately leading to a moment of peril where they lose consciousness.
Once they awaken, the police arrive, but the celebration is short-lived as more giant wasps emerge, wreaking havoc on the unsuspecting officers, as well as on Paul and Julia. Their ultimate fate remains shrouded in uncertainty as the terrifying swarm continues to descend on them.
