This is the story of how I became my sister.

I got the letter on September the first. I remember that because it was the day after our thirteenth birthday. My thirteenth birthday. The first one I wouldn't share with my twin sister, Scarlet.

I woke up and made my way down the winding stairs of my aunt Phoebe's house, breathing in the smell of bacon cooking as I went. The early morning sun was already warming the air. It could have been a good day. As I emerged from the shadow of the stairs and into the sunlit hallway, I noticed it. An envelope lying on the stone floor.

For a moment I thought it might be a belated birthday card - the only card I'd had that year was from my aunt, and looking at the single, lonely name written at the top had hurt more than I could say - but as I picked the envelope up it felt more like a letter.

Scarlet had always liked to send me secret messages, but she sealed her letters so haphazardly that you could probably have opened hers just by breathing on them. This one was closed tightly and sealed with wax. I turned it over and saw that it was addressed to my aunt. I ought to open it, I thought. Aunt Phoebe didn't object to me reading her post. In fact, it was usually necessary; she just let it pile up in the hallway if I didn't.

I went into the kitchen and sat down on one of the rickety chairs. I took a closer look at the seal on the envelope - it was black, with a raised imprint of a bird on top of an oak tree. The words 'Rookwood School' were stamped underneath in dark-coloured ink.

Rookwood School. Scarlet's school. Why were they writing to Aunt Phoebe? I slid a butter knife from the drawer along the envelope.

Mrs Phoebe Gregory

Blackbird Cottage

Bramley Hollow

30th August, 1935

Dear Mrs Gregory, As you are the guardian of Ivy Grey, I am writing to inform you that in light of recent unfortunate circumstances a place has become available at our school, and your niece will take it. Her parents have fully paid the fees and she is due to start as soon as possible. A teacher will be sent to collect her and the details will be explained upon her arrival.

Regards, Edgar Bartholomew (Headmaster)

I threw the letter down as if it had singed my fingers. Could they really be referring to my sister's death as 'unfortunate circumstances'?