Scotland, 1949: Caroline Gillan and her new husband Alasdair have moved back to Kelly Castle, his dilapidated family estate in the middle of nowhere. Stuck caring for their tiny baby, and trying to find her way with an opinionated mother-in-law, Caroline feels adrift, alone and unwelcome.

But when she is tasked with sorting out the family archives, Caroline discovers a century-old mystery that sparks her back to life. There is one Gillan bride who is completely unknown - no photos exist, no records have been kept - the only thing that is certain is that she had a legitimate child. Alasdair's grandmother.

As Caroline uncovers a strange story that stretches as far as the Arctic circle, her desire to find the truth turns obsessive. And when a body is found in the grounds of the castle, her hunt becomes more than just a case of curiosity. What happened all those years ago? Who was the bride? And who is the body...?