Two years after choosing not to kill the man who killed his son, former police sergeant Leo Barnes is now head of security for Senator Charlie Roan, a presidential candidate targeted for death on Purge night due to her vow to eliminate the Purge. The New Founding Fathers of America (NFFA) see her as a threat to their rule and lift the tradition of granting immunity to government officials during the annual Purge. With no protection on the one night when all crimes are legal, Leo must protect Senator Roan while navigating a city filled with violence and chaos as they try to survive the night.

Meanwhile, a deli owner named Joe Dixon defends his store against a group of malicious Purge participants after his Purge insurance rates are raised beyond his affordability, with the help of his employee, Marcos, and a Purge-resisting EMT, Laney Rucker. Their paths eventually cross with Leo and the Senator, creating an unlikely band of survivors. Struggling to fend off assassins and fend for themselves on the lawless streets, the group attempts to survive until morning, all the while debating the ethics and necessity of the Purge, as Roan's platform promises an end to the barbaric tradition that has become a cornerstone of the dystopian society.