Is it the air they breathe?
The many children who have died, or are currently sick, from cancer, leukaemia and other life-threatening diseases in South Durban come come from different suburbs, different races, different backgrounds.
Yet they have all breathed the same badly polluted air.
Their parents, too, are united by a common factor - almost unbearable emotional pain and grief.
Are these children - and indeed the older people of south Durban - getting cancer because of the poisonous industrial air which frequently permeates the residential areas of the Bluff, Merebank, Wentworth and Austerville?
Is it motor car pollution? Is it just "coincidence" or is it their genes?
And are the authorities doing enough to find answers?
After several weeks of documentary research, countless telephone calls and hours of interview sessions in the living rooms of cancer victims, many of these questions remain unanswered.
But the evidence does point to a serious problem and the need for urgent and thorough investigation.