In the summer of 1904 Sarah Pollenfax, the daughter of an impecunious clergyman, arrives at Carriglas, an island off the coast of Cork, to act as governess for her distant cousins. It's a magical time in a magical place. But when she comes back almost thirty years later, after the First World War and the Irish Civil War have taken their toll, she discovers that there were things going on during that apparently idyllic summer which now horrify her and which cast a long shadow over the remnants of the family still living there.