All the rules are broken as a sect of lawless marauders decides that the annual Purge does not stop at daybreak and instead should never end as they chase a group of immigrants who they want to punish because of their harsh historical past.

Cancer-terminal tycoon Peter Murdoch's secret Wexel Hall Pharmaceuticals lab has developed a blood orchid extract cure. To examine why it works optimally in snakes, they also bread a super-anaconda strain. But the original pair escapes, leaving a bloody trail of human corpses. Murdoch runs, instructing his staff to clean up. They keep failing and being eaten like unsuspecting locals, some alive, even after enlisting ruthless big game hunter Hammett. The fast-growing pregnant monster sheds its skin, thus disabling the only tracking device they have.