May, 1831, and on a tiny island off the Isle of Man a lighthouse provides a harsh living for an unusual family. Lucy and Diya, husbandless and with three children between them, watch over the ancient light on Ellan Bride. Meanwhile the Scottish engineer, Robert Stevenson, is modernising the nation's lighthouses, and Ellan Bride and the future of the family, are under threat. When two surveyors arrive to assess the light, tension escalates to danger point.