Fergal is helping his mother nurse a bedridden woman on a Yorkshire farm. In his free time he roams the hills and dales, and there meets a girl, Alex, sensing at once the peculiar obsession with the nearby reservoir that grips her and everyone else in the valley. As rainless heat settles over the parched land, everyone is watching the reservoir, seeing the water level fall day by day and waiting - as if something undefinable will rise from its depths. The undercurrents threaten Fergal too, with memories of his failure to help a drowning friend, and his belief that soon he will have to help Alex. This time he must not fail.