Finn and Cara are brother and sister and live on the Irish coast, where sheep graze on the green cliffs, wind howls in the chimney and grey fog rises up above the sea.
One day, when the siblings are out rowing their boat in the bay, thick fog suddenly closes in around them and the current washes them upon an unknown beach. Finn and Cara have landed on Fog Island, from which no one has ever come back alive.
But they do not lose heart, and end up meeting the wondrous master of the island. From him, they learn where the fog comes from.