Mercy and her sister Charity have never questioned their daily routine, each day unfolding exactly as the next. They live at night, sleep during the day and see their widowed father only rarely - their house shrouded in perpetual winter. Then one day, Mercy is woken to find a snowdrop on her pillow. A sign of spring, a subtle hint at a possible different future. A chance meeting with the mysterious Claudius sets her to questioning everything she has ever known - not least the truth behind her mother's death. Bit by bit Mercy traces her parents' story through the past, travelling back to see herself as a young child, silent witness to the dramatic events Claudius himself plays an enormous part in - only when she has pieced together the truth can her world begin to move on.