Doctors at Antwerp's National Institute for Contagious Diseases discover a patient infected with a contagious and deadly disease, and the authorities take no chances and seal off the centre of the city for 48 hours to prevent further spreading of the virus. Lab assistant Jana, police officer Jokke, pregnant Ineke, teacher Katja and her class and the ambitious Dr Cannaerts are among those who find their lives turned upside down by the quarantine.
Katja makes a grisly discovery in a restricted area of the National Institute for Infectious Diseases, Lex is asked to attend a press conference held by the minister of public health at which Leo asks why 5,000 people are being contained after the death of just one person with flu like symptoms.
Quarantine has been prolonged and certain food products are starting to become scarce within the cordon. Lex starts organising food distribution via the container sluices. Leo has asked his friend Ingrid to provide a video diary from within the cordon, but soon realises the enormity of the tradegy unfolding when Ingrid films the death of her own girlfriend struck by the lethal virus.
Katja is shattered by the loss of Thomas, whose death at the food distribution point has led to more contamination, and NIIDA is swamped by an influx of new patients. Lex is given army support for the security of the cordon, but he and his men are at breaking point when all leave is cancelled.
Day 12 of the cordon, and the flimsy fabric of society is beginning to break down. Jokke is unable to prevent black marketeers taking over the distribution of food, and the situation is inflamed when Lommers takes the drastic action of blocking phone signals to the cordon. Katja is wondering when Dr Cannaerts is going to make public the deaths of two of his staff from the institute.
Day 16: Leo and Lex examine the CCTV footage from security cameras at the institute which Jokke has managed to smuggle out of the cordon via the sluice. Leo's suspicions are even further aroused when Lommers herself pays him a visit in an attempt to silence his 'Horseman' blog. An unfortunate encounter with a carrier of the virus by one of Katja's young charges leads to horrific consequences.
With tension inside and outside the cordon intensifying, Dr Cannaerts has an untried vaccine smuggled into NIIDA. When Lex is called to a breach in the cordon security he and Lommers are quarantined together, where Lommers lets slip about the pressure of working on disaster scenarios.
Eager to find out what Lommers is concealing, Lex breaks into her office and discovers a concealed USB stick, but what it holds is so explosive that even Gryspeerts is reluctant to put it on his blog. Thinking that she has found a refuge with her friend Melissa, Ineke suggests they try to find the lab that Jokke has told her about, but conditions at the F Tron offices are reaching breaking point.
After the brutal raid on the lab, Jana is desperate to get away and finally agrees with Sam to attempt the escape route being controlled by the black-marketeers. Jokke and Lien hear rumours of a boy who is immune from the virus. Lex calls on Gryspeerts wondering why he has not published his explosive evidence, but he himself comes under pressure from Lommers.
Totally discouraged, Jana succumbs to Sam's offer of an escape route from the cordon. At NIIDA, Jokke does his utmost to reveal the full truth about the virus. Lex and Nald discover a hole in the cordon and set out to find the people behind it. The discovery leads to Lex having to make the biggest decision in his life.