Catering business owner Julia and her subordinate Paul are traveling to an isolated mansion in New York to cater a small party for Mrs. Perch, and her son Sydney, honoring their family's dead patriarch. Among the guests in the party are the town's mayor Caruthers. Soon, mutated, deadly wasps begin attacking, and killing party guests. In the process, Paul, and Julia realize that the wasps reproduce through stings, causing giant wasps to birth out of humans, and killing the host. Only Paul, Julia, Caruthers, Sydney, Mrs. Perch, and cook Flora escape into the house.
With the phone lines dead due to a car crash outside the house, preventing the survivors to call the police, they decide to hide out in the basement. However, Mrs. Perch is revealed to be stung, and a giant wasp births from her body, killing her. Flora is also killed, and Paul, Julia, Caruthers, and Sydney escape to the basement. They decide to escape in the catering van, although Paul has left his keys outside. He manages to retrieve the keys, killing a wasp in the process, although Sydney is also revealed to be stung, and a wasp births from his body, and begins controlling him before Paul, and Julia subdue him.
Paul, Julia, and Caruthers begin sneaking around the house to an exit, although Caruthers is killed by a wasp before Paul, and Julia escape into another room. They kill an invading wasp, and make it outside, although Paul is abducted by a wasp, and taken to a nest controlled by the wasp Mrs. Perch birthed. As she is about to have Sydney inject a larvae into Paul's mouth, Julia arrives, and kills him before rescuing Paul, and blowing up the nest. As they drive away, one flaming wasp attacks the car, and Paul plans to ram the car into a tree to kill the wasp, although Julia refuses to leave, and the two crash the car, killing the wasp, and knocking them unconscious.
Paul, and Julia awaken sometime later, and the police arrive; they begin having sex in the back of an ambulance. However, it is soon revealed several giant wasps are still alive, which begin killing the police officers, as well as Paul, and Julia, and their fates are left unknown.