Josh Lucas, foreground, in “The Forever Purge.” Jake Giles Netter/Universal Pictures

“The Forever Purge” is bookended with scenes of families making their way across the U.S.-Mexico border. As it opens, Adela and her husband, Juan (Ana de la Reguera and Tenoch Huerta), are being escorted by a guide, known as a coyote, into Texas from Mexico, where they’re fleeing cartel violence by cover of night. By the end of the film, it’s the other way around: Crowds of Americans are thronging the border, clamoring to get into Mexico.

What the heck happened in between?

It’s a topsy-turvy world in this fifth installment of the “Purge” horror franchise, which takes place in a dystopian future in which the American government has instituted an annual, 12-hour, overnight “blood holiday,” called the Purge, during which all crime – including murder – is temporarily legal. It’s like an emotional sinus flush, or so the thinking goes, cleansing the pent-up mucus of rage some of us carry around in our heads so that we can all breathe easier – or at least those of us who imagine that killing someone would accomplish that.

Ew.

Yes, ew. As with the other films, there’s plenty of bloodletting here, shown in often gruesome close-up, and with an occasional creative touch. But there are a couple of differences between this chapter of the saga and the previous films: For one thing, when the Purge depicted in the first half-hour of the film has ended – after what most law-abiding citizens refer to as a “lockdown,” giving a creepy new meaning to a term that’s lately become commonplace – the Purge doesn’t end. An underground network of violent nationalists, united under the slogan “Ever After,” has decided to “purify” the country of anyone other than natural-born Americans, whatever that means.

In this film – which struggles to justify its lurid fascination with mayhem by burnishing the plot with a patina of class and racial awareness – that means they start with the undocumented Mexican immigrants. Juan, who has taken a job as a ranch hand working for the wealthy Texas Tucker clans, whose scion Dylan (Josh Lucas) is a thinly veiled bigot, is soon running for his life. Not from the Tuckers, several of whose grateful lives he saves when a disgruntled worker kills the family patriarch (Will Patton), but from the leader of the local Purification faction (Jeffrey Doornbos).

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Juan, Adela, Dylan and his family have soon joined forces and begin making a beeline for the border, where the Mexican government, in a spirit of altruism, has declared a six-hour border amnesty for Americans – and anyone else – who wants to get the heck out of Dodge. Can you feel a kumbaya moment coming?

Not so fast.

There’s a gauntlet that still needs to be run, through “Mad Max”-style marauders in goggles and leather, and riding souped-up ATVs with military-grade weapons. This is, after all, Texas.

There’s a nugget of … maybe not wisdom, but something gristly worth chewing on here, if you have the stomach to stick your hand into gaping intestines, pull it out and wipe off the blood. I wouldn’t call it food for thought, but it gives “Forever” a slightly higher nutritional value than some of its predecessors. It’s a question whose answer is obvious, but it’s still worth asking. Who are the real Americans here: the self-described “patriots” running around shooting people, or the people who, with or without a green card, are willing to help their neighbors?

From left, Josh Lucas, Ana de la Reguera and Tenoch Huerta in “The Forever Purge.” Universal Pictures