A new virus strain has infected rice crops in East Asia causing massive famine; the virus is also revealed to be found in the UK but because of its selectivity does not affect the country's agriculture. After the introduction of a new pesticide, developed in preference to breeding resistant crops, a mutated virus appears and infects the staple crops of West Asia and Europe such as wheat and barley—all of the grasses (thus the novel's title). It threatens a famine engulfing the whole of the Old World, while Australasia and the Americas attempt to impose rigorous quarantine to keep the virus out.