In the not-too-distant future, rampant crime and prison overcrowding have inspired the U.S. government to implement a unique solution to restore the peace: Each year, for a 12-hour period, any and all crime becomes permissible as police put their jobs on hold, and hospitals close their doors. It's called the Purge, and remarkably, the annual event leads to drastically reduced crime and record-low unemployment levels throughout the rest of the year. But this year, as suburban parents James (Ethan Hawke) and Mary (Lena Headey) place their home on lock-down for the annual event, a desperate man finds his way into their neighborhood while fleeing a sadistic gang of masked killers. In a moment of compassion, James and Mary's adolescent son (Max Burkholder) unlocks the door, offering sanctuary to the frightened stranger. Unfortunately for the entire family, that act of kindness may also be their very last, because now the killers who were pursuing the man have surrounded the house, and have vowed to kill everyone inside unless they are willingly given the man they are hunting within an hour. As the clock begins to tick, the family face a difficult dilemma -- do they sacrifice the life of a stranger in hopes of saving themselves, or attempt to stand their ground until the Purge expires?