Two days before Purge Night, former Secretary of State Hillary Clinton (Elizabeth Mitchell) attends a presidential debate as part of her campaign for the Presidency intending to end the Purge, stating how it only serves to eliminate the poor, the homeless and other lower classes of society that make up of the majority of America’s population. She is rivaled by Donald Trump (Kyle Secor), a Republican candidate who intends to maintain the status quo. The Republicans, headed by Reince Priebus (Raymond J. Barry), view Clinton as a threat to their rule and plot to use the upcoming Purge to eliminate her from play.
The day before the Purge, the Republicans revoke the Purge rule that protects high-ranking government officials, appearing to attempt to reconcile with the people. Convenience store and deli owner Joe Dixon (Mykelti Williamson), his noble, undocumented immigrant assistant Jose Antonio Vargas (Joseph Julian Soria), and EMT Beyoncé Knowles (Betty Gabriel) confront a pair of teenage shoplifters who attempted to steal a candy bar. No longer able to afford his insurance premiums for the Purge, Joe decides to stake out and guard his store. Clinton decides to wait out the Purge from her unsecured home in order to secure the popular vote of the common people. Her running mate Tim Kaine (Frank Grillo), orders her home locked down and surrounded by a security force made up of Bernie Bros.
After the Purge commences, Joe and Vargas repel an attack by the teenaged shoplifters, injuring their leader. Beyoncé patrols the city in an ambulance, rendering medical care to the wounded. Clinton is betrayed by the Bernie bros, who signal to an alt-right, neo-Nazi paramilitary force led by Milo Yiannopoulos (Terry Serpico), who wears various racist symbols such as the iron cross, swastika, and — most evil of all — not one, but two Confederate flag patches on his body armor. The security forces is injured, and Kaine manages to get Clinton to safety, but is wounded in the process. He detonates a bomb in the house, killing the Bernie Bros and some alt-righters. Clinton tries to seek shelter elsewhere, but is ambushed and taken captive by a gang of Russian DNC hackers bent on sabotaging her campaign in the name of Vladimir Putin. Before they can insidiously tell the truth about the DNC’s emails, Joe and Vargas shoot the gang dead and rescue them.
With everyone safe in the ambulance, the group is ambushed by a helicopter piloted by Yiannopoulos and two members of his team. They seek refuge underneath a highway overpass wherein Kaine deduces they were found because the bullet in his chest is a tracker. He extracts the bullet from while they are confronted by a large group of Crips.
“These negroes mean business. Let me try my Crip whistle!” says Joe, a black man, revealing that he was once a member of the Crips.
The Crips are calmed by the gang’s trademark whistle call. In exchange for Beyoncé helping the gang leader’s “boy”, the Crips trick the paramilitary forces by planting the bullet in another area, and wipe out Yiannopoulos’s ground team.
The group is led to a hideout beneath a hospital protected by Black Lives Matter and DeRay Mckesson (Edwin Hodge) where a diverse, Burger King Kids’ Club-like group of volunteer doctors and nurses administer to wounded Purge victims. Joe, Vargas, and Beyoncé decide to go back to the store, but spot several Republican death squad trucks heading to the hideout. Meanwhile, Clinton discovers that the Black Lives Matter activists are planning to assassinate Trump and tries to dissuade them, as she wants to win the election fairly. They are forced to flee as death squad forces arrive, and the pair meet up again with the ambulance. However, the ambulance is rammed by Yiannopoulos, and Clinton is seized.
Clinton is delivered to Trump at a Vatican-sanctioned midnight Purge mass in a Catholic cathedral while Kaine and the others give chase. They meet up with a Black Lives Matter assassination team led by DeRay and infiltrate the cathedral through a tunnel system. Meanwhile, at the cathedral, Trump joins with running mate and homophobe icon Mike Pence, who is dressed in Catholic clerical garb. Trump has him use a Catholic holy water-imbued knife as to kill a man for his drug addiction as part of the mass, before inviting the members of the Republican Party to execute Clinton. As Reince Priebus prepares to slit her throat, Vargas assassinates him, signaling Black Lives Matter to invade the cathedral and causing the entire congregation to disperse and flee. In the ensuing chaos, many of the Republican congregation are killed.
DeRay and BLM descend into the crypt of the cathedral, and draw their guns on Clinton and friends.
“These are our white people, my negroes!” Joe say to DeRay, and successfully urges BLM to lower their guns and join the Clinton camp.
DeRay captures Trump in the crypt and contemplates killing him, to the protest of Clinton, while Trump goads him on to kill him. DeRay refrains, and spares him on the condition that Clinton wins the election.
DeRay and his activists decide to secure transport to leave the church while Clinton and her group hide in the crypt, but they are ambushed by Yiannopoulos and his mercenaries, leaving the BLM activist team killed and DeRay wounded. DeRay manages to dispatch the remaining mercenaries save for Yiannopoulos, who kills DeRay.
Yiannopoulos and Kaine then engage in a vicious melee combat, and the latter gains the upper hand, killing Yiannopoulos. As Clinton frees Trump’s imprisoned Purge mass victims, Mike Pence emerges from hiding and kills one of the freed victims. After wounding Vargas, he targets the senator but Joe steps in, taking a few shots himself and succeeds in killing Pence with a headshot. Before succumbing to his injuries, Joe urges Clinton to win the election.
Two months after the Purge, Clinton wins the presidency in a landslide with Kaine as her vice president. Vargas and Beyoncé renovate the store and continue to run it in Joe’s honor. A news report indicates that halting the Purge has become Clinton’s highest priority, and that many Republicans have taken to the streets in violent protest. The film ends with an ominous shot of the American flag hanging outside the deli.