Teacher Kit Chaplin can't understand why some students at his north London school are experiencing an extreme ticking noise in their ears. Perhaps it's just a severe form of tinnitus? But only days later, it spreads to more students - and starts leaving bodies in its wake. Eminent vaccinologist Lilly Slater has never seen anything like this before. She must race against the clock to work out what is happening - and to find a cure. But their investigation throws up more questions than answers until they realise the mystery behind the illness is even bigger than they could have imagined... Will the truth behind this catastrophe become clear before it's too late?