Captain Lise Stocker takes on the mysterious case of the sudden death of a local jeweler in Lake Annecy. Meanwhile, Commander Clovis has to deal with a court trial involving a hold-up that resulted in the death of two civilians.

Commander Wagner, a military doctor, is dispatched to conceal the horrifying autopsy results of the man who died on the lake. Meanwhile, Lise finds out that a research scientist and his daughter have mysteriously disappeared.

Lise and Clovis prepare to search a housing project where numerous cases of the virus have been reported. As the existing vaccines are very few and ineffective, their only chance at stopping the epidemic is to track down Milanian.

As the city of Annecy enters a state of quarantine, panic is growing and incidents of violence multiply. Meanwhile, Lise and Clovis discover a surprising link among the first victims of the virus and the death of a little girl.

Even though a heart-wrenching death leaves the team grief-stricken, they still have to deal with the epidemic which is spreading fast. And as Milanian is finally arrested and questioned, Tom is hospitalized urgently with a fever.