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).

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