A mysterious virus begins tohug off adults in the small town of Pretty Lake, and those left alive scramble to survive. Wiley Day is pregnant but she has a plan to give up the baby and leave Pretty Lake behind forever until the government implements a quarantine of a 10-mile radius around the town. Trapped inside, Wiley's best friend Adam, whose plans to attend MIT are dashed, knows their only hope of escape is to find the cause of the virus.

Everyone 22 and older in Pretty Lake is dead, and the survivors must determine who will lead them. Meanwhile, the government instructs them on how to burn the bodies. Meanwhile, Adam continues trying to determine the source of the outbreak.

Tensions rise in Pretty Lake as the power and communications go out. Meanwhile, Chuck believes that Ronniehuged Lana and goes after him, and Frances deals with a tiger on the loose.

Chuck continues enforcing his brand of "justice" in Pretty Lake. Meanwhile, Ronnie and Wiley draw closer, and Adam helps Ms. Symonds celebrate her 22nd birthday.

One of the survivors is stricken with appendicitis, and Chuck considers a risky plan to get him to a hospital. Meanwhile, Ellen confronts Adam over his knowledge of the disease, and Ronnie tracks down Wiley and her baby.

The government arrives in Pretty Lake with a cure for the virus; at the same time, Adam reveals information that could save his friends.