During construction at the old, hard-pressed Lakewood Hotel, two workers stumble upon a swarm of ants in a closed section of the building. After discovering the unusually aggressive and dangerous ants, the workers attempt to get the warning out, but they are accidentally buried alive. Shortly after, the unscrupulous real estate magnateAnthony Fleming and his partner and mistress Gloria arrive at the hotel, there to haggle with the elderly proprietor, Ethel Adams, and her daughter Valerie as they pursue plans to convert Lakewood into a casino. In the meantime, foreman Mike Carr, who is in a relationship with Valerie, and his co-worker and friend Vince find the two missing men, but dead from poisoning. The ants begin to emerge, attacking a boy, then killing a hotel cook. They nearly kill Vince as he and Mike investigate the pit in which their men were buried. Peggy Kenter, a Board of Health inspector and an acquaintance of Carr's, decides to quarantine the hotel, thinking a virus is at work. But Mike soon discovers that there is an immense ant nest in the pit, and concludes that these insects are responsible for the attacks. Tom, a BOH researcher, finally discovers that the ants are highly poisonous and resistant to insecticides. By that time, the ants are swarming the hotel by the millions, killing Gloria and Peggy's assistant White and driving Carr, Valerie, Ethel, Fleming, hotel employee Richard and his girlfriend Linda upstairs. Vince alerts the authorities, who attempt to contain the ants with a trench - filled first with water, then with burning gasoline after Tom points out that army ants cross streams on bridges built from ant corpses - and rescue most of the trapped people inside the hotel. Carr, Valerie and Fleming, the only people remaining, are eventually cornered by the ants; Tom tells them not to move, in order to give the ants no reason to attack them. As the ants begin crawling all over them, Fleming launches himself from the room's balcony into the swimming pool below, in a desperate attempt to escape, and dies in the fall. Shortly afterwards, two suited-up rescuers arrive and take Carr and Valerie to safety. When they are taken away by the ambulance, Tom assures Carr that such a case will not likely be recurring, as the unique environmental conditions at the hotel estate were vital for the existence of the ants' nest.
