Emergency physician Drake Cody is on duty at a controversial oil pipeline's opening ceremony when an explosion critically injures a Minnesota senator and others.
With the blast, sovereign citizen militia leader Tolman Freid, cruelly wronged by government and corporate injustice, has transformed his extremist anti-government ideology into terrorist action. He believes he is history- and duty-bound to take down the system, no matter the cost.
Upon arriving at the ER, Drake's hopes for saving the dying senator and other victims rise, but in the next minute, Freid and his militia set in motion the rest of their devastating scheme—a terrorist action more deadly than any in history—and it is centered in the ER.
While FBI agents and police coordinate desperate efforts outside the hospital, Drake, a few ER colleagues, and a handful of vulnerable patients must somehow stop the heavily-armed, fanatical extremists or they and tens of thousands of innocent people will die.