Teenaged sisters Emma (Sofia Black-D' Elia) and Stacey (Analeigh Tipton) live a normal life, until their small suburban neighborhood is stricken with a mysterious parasitic virus. As the disease rapidly spreads throughout the town, the two band together to barricade themselves from infection. But it may already be too late – when the virus enters their home, the sisters are faced with an impossible choice: protect each other, or survive the virus.