In the New Mexico desert, Police Sgt. Ben Peterson and his partner find a child wandering in the desert and soon they discover that giant ants are attacking the locals. FBI agent Robert Graham teams up with Ben and with the support of Dr. Harold Medford and his daughter Dr. Patricia 'Pat' Medford, they destroy the colony of ants in the middle of the desert. Dr. Harold Medford explains that the atomic testing in 1945 developed the dangerous mutant ants. But they also discover that two queen ants have flown away to Los Angeles and they are starting a huge colony in the underground flood control tunnels of that city. When a mother reports that her two children are missing, the team begin searching for them. Will they arrive in time to save the children and destroy the colony?