Detective Lindsay Boxer is jogging along a beautiful San Francisco street as a ferocious blast rips through the neighbourhood. A townhouse owned by an internet millionaire explodes into flames, three people die and a sinister note signed 'August Spies' is found at the scene. Soon a wave of violence sweeps through the city - and it seems that whoever is behind it is intent on killing someone every three days. Even more terrifying, the four friends who call themselves the Women's Murder Club discover that the killer has targeted one of them. And Lindsay learns that one member of the club is hiding a secret so dangerous and unbelievable that it could destroy them all.