During a month’s stay in their holiday cottage in Mull, the MacDonalds and their three children conscientiously strive to be kind to a moody teenage guest, Kate. Though she has come up from London, Kate is proud of her O’Neill antecedents on Barra, and prefers to be called Bridie. Despite the MacDonalds’ good intentions, she does not fit in well. After a disquieting excursion to the ancient hill fort of Dunadd, a nocturnal time-shift occurs and the four teenagers are transported through the years to the forests and mosses of sixth century Dalriada. Their identities begin to fuse strangely with their Scottish tribal predecessors. The old faith is being challenged by the incoming Christianity of Columba on Iona; there are fierce battles; and Bridie begins to emerge as the tribal priestess...