On October 6, 1971, an American combat medic, Jacob Singer, is with the 1st Cavalry Division (United States), deployed in a village in Vietnam's Mekong Delta, when his close-knit unit comes under sudden attack. As many of Jacob's comrades are killed or wounded, others exhibit abnormal behavior with some suffering catatonia, convulsions, and seizures. Jacob flees into the jungle, only to be bayoneted by an unseen assailant.