When a mysterious virus strikes the population of Montreal, Anne-Marie Leclerc, head of the Emergency Public Health Laboratory, whose mission is to identify the causes of public health crises and to help authorities deal with situations as they arise (bioterrorism, lethal contagion, mass poisoning etc.), is the first line of defense against an epidemic causing numerous deaths. Since misfortunes never arrive singly, Anne-Marie also discovers that her husband Marc, an emergency physician and the father of her 16-year-old daughter Sabrina, is having an affair with another doctor, Chloé. Anne-Marie must collaborate closely with this newly-formed couple to combat the epidemic while her daunting task of stopping the spread of the virus is complicated by the Minister of Public Security, Laurent Demers. The main characters must face fears and dilemmas that are very present in the real world. It’s through the eyes, ears and hearts of these characters – people very much like ourselves – that we experience the epidemic.