The Purge is a high-concept blunt instrument of a thriller, a movie that offers a straightforward set-up and few subsequent surprises. It does exactly what you expect and doesn't really go anywhere you don't assume it will.
The premise is devilishly simple: In the future, the government has eliminated violent crime (or any other kind, for that matter) by legislating one night a year when anything goes. The designated 12 hours - 7 p.m. to 7 a.m. - are referred to as the Purge, when all crimes are allowed, including murder.
Ethan Hawke plays James, who lives in a suburban gated community with his wife, Mary (Lena Headey), and their two kids, Charlie (Max Burkholder) and Zoey (Adelaide Kane). James, as it happens, sells security systems, which allow him and his neighbors to lock down their houses on Purge night. Indeed, he's the top seller in his company, having sold to almost everyone in his community.
After a half-hour of expository set-up to establish who James, Mary and their kids are (but not in any way that will lead to something interesting), we get to the lock-down moment. But there's an intruder who, unbeknownst to James and his family, has had himself locked into the house with them. Seemingly more of a threat is the fact that James' young son, who seems upset by watching live streams of security cameras showing Purge activities from around the country, lets a stranger into the house after lockdown.
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