One night, Annie went missing. Disappeared from her own bed. There were searches, appeals. Everyone thought the worst. And then, miraculously, after forty-eight hours, she came back. But she couldn't, or wouldn't, say what had happened to her.

Something happened to my sister. I can't explain what. I just know that when she came back, she wasn't the same. She wasn't my Annie.

I didn't want to admit, even to myself, that sometimes I was scared to death of my own little sister.

Now. . .

The email arrived in my inbox two months ago. I almost deleted it straight away, but then I clicked OPEN:

I know what happened to your sister. It's happening again . . .