At a top secret U.S. government facility codenamed Area X, cellular biology professor and Army veteran Lena is questioned after returning as the sole survivor of an expedition to an anomalous zone known as the "Shimmer". Three years prior, the Shimmer emerged from a meteor that landed inside a lighthouse on the coast of the southern United States, and is gradually expanding its boundaries. Lena's husband Kane, a Green Beret, was part of an earlier expedition and reappears at their home after a year of absence, unable to explain where he was or how he came back. His condition quickly deteriorates and Lena calls an ambulance, but they are intercepted by security forces and taken to Area X. With Kane in intensive care, a government psychologist, Dr. Ventress, shows Lena the Shimmer and explains that many exploratory teams have entered, but only Kane has ever returned. Ventress prepares to lead a new scientific expedition into the Shimmer, consisting of Lena, physicist Josie Radek, geomorphologist Cassie "Cass" Sheppard, and paramedic Anya Thorensen.