It is March 21, 2023, hours before the annual Purge event. While television programs credit the Purge for record low unemployment and poverty levels, people across the country are preparing either to commit acts of violence or to barricade themselves indoors against the mayhem. Meanwhile, an anti-Purge resistance group intermittently hacks into television programs to broadcast their own messages that challenge the system, stating that the Purge does not cleanse aggression, but rather eliminates the poor from the population.
2023年，殺戮日開始的兩個小時前，在洛杉磯市區中，女服務生伊娃在工作結束、與自己最好朋友譚尼婭說再見後回了家，女兒凱莉當時正迷上網絡上的一個殺戮日反抗組織的視頻，而組織領導人卡梅隆在視頻中強調自己與手下人早就看不慣這些所謂的新開國元勳與富人們在殺戮日的夜晚時在自己平安的家中享受天倫之樂、卻將普通市民放在外自生自滅。在城市的另一端，警察中士李歐·巴恩斯在家中準備武器、身穿防彈衣、不顧自己前妻的警告而開著一輛加固警車打算利用這場夜晚去殺一個他最憎恨的人。一對年輕夫妻夏恩與麗茲在汽車拋錨後被困在無人經過的高速公路上，後來被一群臉上化妝、紋身與戴面具的軍團追殺，兩人在無處可去下只能往市中心跑。