The Purge: Anarchy Frank Grillo, Carmen Ejogo, Zach Gilford. Directed by James DeMonaco. Rated R. Opens Friday.

Last year’s The Purge took an intriguingly ridiculous concept (in a future America, all crime is legal for one 12-hour period a year) and wasted it on a fairly standard home-invasion thriller, ignoring most of the possibilities of this messed-up, highly implausible political allegory. Writer-director James DeMonaco expands on his ideas a bit in the sequel The Purge: Anarchy, but most of the potentially fruitful explorations are eventually tossed aside in favor of more firefights and foot chases.

While the first movie took place in a wealthy suburb, Anarchy is set in the center of an unnamed city, where a group of people find themselves stranded outside as the purge begins. The setting offers an opportunity to explore how the annual orgy of violence reflects class differences, but as in the first movie, DeMonaco’s efforts at social commentary are half-baked at best, and his most promising addition, a charismatic anti-purge activist (Michael K. Williams) who’s trying to foment a revolution, barely gets any screen time.

The movie’s main characters spend the majority of the time running from various gangs that are out to kill them, with very little variation in the peril. Late in the movie, DeMonaco throws in a gathering of wealthy people who capture the unsuspecting poor to hunt in a controlled environment, but by that point, the monotony of the action has overtaken any potential for real suspense. The movie ends by starting the countdown to the next purge, but if Anarchy is any indication, DeMonaco is already pretty much out of ideas.