Think you know the person you married? Think again…

Things have been wrong with Mr and Mrs Wright for a long time. When Adam and Amelia win a weekend away to Scotland, it might be just what their marriage needs. Self-confessed workaholic and screenwriter Adam Wright has lived with face blindness his whole life. He can’t recognize friends or family, or even his own wife.

Every anniversary the couple exchange traditional gifts – paper, cotton, pottery, tin – and each year Adam’s wife writes him a letter that she never lets him read. Until now. They both know this weekend will make or break their marriage, but they didn’t randomly win this trip. One of them is lying, and someone doesn’t want them to live happily ever after.

After years of avoiding each other, Daisy Darker’s entire family is assembling for Nana’s 80th birthday party in Nana’s crumbling gothic house on a tiny tidal island. Finally back together one last time, when the tide comes in, they will be cut off from the rest of the world for eight hours.

The family arrives, each of them harboring secrets. Then at the stroke of midnight, as a storm rages, Nana is found dead. And an hour later, the next family member follows…

Trapped on an island where someone is killing them one by one, the Darkers must reckon with their present mystery as well as their past secrets, before the tide comes in and all is revealed.