After two people fall unconscious in a city center from an unknown illness, Tracy, a public health official, and emergency services try to locate the source of the deadly nerve agent that caused it.

CID officer Nick Bailey’s condition worsens as Tracy struggles to protect local residents against the numerous deposits of Novichok being found across the city.

As the city is starting to heal, a scavenged perfume bottle leads to tragic consequences for Dawn and Charlie.

As the city struggles with renewed panic, Tracy learns that the contamination might be worse than she before.