When a pet cat, affected by rabies is smuggled into Britain, the spread of the disease among the animal population goes undetected - until the first human falls victim to the terrible Mad Death.
Hilliard moves quickly to contain the rabies outbreak inside the Infected Area while Anne desperately attempts to trace the source of the virus in order to save others the agonising death she has seen one of the victims suffer. Then another case is reported outside the Infected Area.
A deliberate act of sabotage jeopardises the containment of the rabies outbreak. Hilliard's life is threatened as he attempts to control the new danger, and Anne's human concern leads her into terrifying danger.