Mercy and her sister Charity live in a twilight world, going to bed just as the sun rises. Their house remains shrouded in perpetual winter, each day unfolding exactly the same as the last. Mercy has never questioned her widowed father about the way they live- and why- until one day, she wakes up to find a snowdrop on her pillow: a first sign of Spring- and a nod towards a new future. A meeting with the mysterious Claudius unsettles Mercy and starts her on a winding path through the family's history, unearthing clues about her mother's death and their house frozen in time.