Rancher Cole Hillman seeks the help of college president Elgin Clark to combat thousands of rabbits that have invaded the area after their natural predators, coyotes, were killed off. Elgin asks for the assistance of researchers Roy and Gerry Bennett because they respect Cole's wish to avoid using cyanide to poison the rabbits. Roy proposes using hormones to disrupt the rabbits' breeding cycle and takes some rabbits for experimentation. One is injected with a new serum believed to cause birth defects. However, the Bennett's daughter Amanda loves the injected rabbit, so she switches it with one from the control group. Amanda is then given the injected rabbit as a pet, but it soon escapes.