You've Just Got to Read This Murder Mystery Book - In a Dark, Dark Wood

We meet Nora as she's lying in a hospital bed trying to regain her memory. All she knows for certain is that there are policemen outside her room and that they are now investigating a car accident. Soon that accident becomes a murder investigation. The police will not tell her which of her friends is dead or what role she played in it.

Nora spends most of the book in her hospital room. We learn the story through her attempts to remember the accident. 

She is a writer who lives in London and has a comfortable, but predictable life. Her morning runs take her outside to challenge her body and emails from her editor challenge her mind. One morning an email from a stranger named Florence puzzles her. She is hosting a hen party for Clare, would Nora please, please come. It would make everything perfect.

Nora has not spoken to Clare in ten years. After an upsetting end to a relationship, she finished her exams and transferred to another school. Clare is the only person in the entire world who knows the reason for the breakup. Nora has no desire to face this. In the ten years since the breakup, she has not dated anyone. Nora also cannot understand how her attendance will make the hen party perfect. 

Her instincts tell her not to go. Seeing Clare will not make anything better. However, Nina lives in London and the two have remained close friends. Nina, who is unaware that Clare and Nora share a secret, convinces her that the two should go.

Ruth Ware deftly increases the suspense. Each hen party game reveals a new secret or slander. Clare continues to manipulate her friends, but they are older and just a little wiser. They no longer stay silent against her barbs. Florence becomes more shrill as the guests assert their independence. Everyone becomes more frightened as mysterious footprints appear in the snow.