The Catherine Storr is called "Thursday". One summary is "A fifteen year old girl tries to help an emotionally disturbed boy", but others refer to the ambiguity about faery. As I recall, drugs were involved.
I have also discovered that Storr committed suicide, which seems awful, as she had written about the dark places, and I would have thought that would have been a defence. She was apparently unhappy about a number of rejections.

Penny