Orphaned Eliza Dunlop has been working as a companion to a rich but cantankerous old lady, Miss Gregory. When Miss Gregory dies, Eliza is found a new position by the old lady’s lawyer, the oily Mr Humbie. She moves to Fife to take up the job as companion to a young lady, Catriona Stuart, but the situation strikes her as unusal. Why does the housekeeper Mistree Kilbain feel like a jailer? Just who is the mysterious Catriona Stuart? And what role does she have to play in an elaborate plot?