Charlie gives Dawn a bottle of perfume, unaware it contains more of the toxin. She collapses and is rushed to hospital within minutes of spraying herself with it. Nick is keen to get back to work but is still struggling with the trauma he went through, while Tracy's faith that the worst had passed is shattered as the team races to discover what else has been missed.

As the city struggles to cope with the renewed panic, Tracy learns that the contamination radius might be even bigger than last time. The second poisoning outbreak is much worse than the first, the random discovery means the poison could be anywhere.

Tracy Daszkiewicz and Supt Dave Minty watch the bodycam footage of DS Bailey walking round the Skripal house and finally make a breakthrough, when they realise he and the Skripals were contaminated by Novichok placed on the front door of the house. As Nick fights for his life, his wife Sarah is beside herself with worry, but tries to remain calm for their daughters. 

On March 4, 2018, emergency services descend on Salisbury city centre where they find former spy Sergei Skripal and his daughter Yulia unconscious on a park bench. They are taken to hospital where doctors struggle to diagnose the source of their illness, while DS Nick Bailey decides to investigate the Skripals' home for further casualties, but soon after returning to work he too begins to feel ill.