When Jinhyun was a child, her life changed when she became part of a new family. She quickly grew close to her new stepbrother, Seungwoo, and secretly fell for him.
To her surprise, Seungwoo seemed to have feelings for her too. But as the years passed, everything changed. Now that Jinhyun is an adult, Seungwoo treats her only as his beloved younger sister, while their younger stepbrother Jungwoo remains a difficult but caring sibling.
One Christmas Eve, the three of them unexpectedly find themselves alone together at home.
With old feelings, hidden secrets, and family tensions coming to the surface, can they make it through the night without anything going wrong?