This Christmas we broke with tradition. I spent it in Cornwall, which is customary, and my sister spent it in Jamaica, which is not. It was very strange, thinking that while I basted the goose, she was probably helping her grandmother skewer a whole goat on to a spit. I say her grandmother because a joint Christmas isn't the only thing we don't share.
When my parents adopted Debs in 1966, they meant well - as I'm sure did all the other white couples from comfortable economic circumstances who played their part in the late Sixties wave of adoption.
The focus then was on the adult. (Today's policy of finding parents for children is relatively recent - until the early 1980s, the emphasis was on finding children for parents, not a subtle difference at all when you think about it.) Black babies were routinely placed with white families, the agencies only too relieved to find them loving homes.
Today, that thinking has grown up. So - with difficulty - have its casualties. It has taken a long time for me to concede that my sister is a casualty, especially as her adoption was always supposed to be the very opposite of an accident. Only now that we are working on the book am I beginning to accept that the whole thing has really been a bit of a disaster.
I used to believe what my mother believed: that love conquered everything, even race. I used to think that she and my father were visionary in their approach, but now I'm afraid they were just colour blind. (Their marriage ended in 1972 and my mother died in 1993 so I am not being as ruthlessly outspoken as I might sound.)
I was the second child and first daughter of responsible and caring people who wanted a third baby. Rather than risk another precarious pregnancy, they gave a home to a child who needed one - not a particularly unusual story for that time.
Debs was under two and I was not yet four when she came to live with us permanently. My parents tried to put her in a cot in their room, but she had already decided she was sleeping with me so we topped and tailed in a single bed for the first night - and for the next two years, until our legs got in the way. Then we had bunk beds which we insisted on keeping until well into our teens. We had a pulley system for note-passing after lights out.
I can barely recall one single allusion to the colour of her skin, nor can I remember ever thinking it was in any way unusual - which is extraordinary considering that we grew up in rural Somerset where black faces were few and far between. There is one isolated memory. We were on swings in a village playing field when my mother overheard a fat boy on a climbing frame call my sister a "blackie". Mum walked up to the boy and told him calmly, "Black is beautiful, which is more than I can say for you. Now I'd like you to apologise." I think it sticks out because it seemed such a crime for anyone to mention the colour thing. It was like the last taboo.
Debs alluded to it, though. Her favourite game aged eight was to pretend we were grown women with children of our own. My imaginary husband was called Cliff, as in Richard, and hers was Johnny, as in Mathis. The singer of When A Child Is Born as pictured on the front of a Christmas LP we had was the only black male she knew.
As a child, Debs wasn't just the beautiful one. She was also the brave one - the one who jumped from the highest branch, dived from the top board. As a teenager, she grew the bigger breasts, started her periods first, kissed a boy before I did.
Her colour made her something of a local celebrity. Pictures of her appeared in the weekly press, snapped at a school fete or on the beach during a heat wave. Like the adoption manuals said, jealousy was an ingredient in our upbringing, but not only hers towards me. I was proud too, though. We were a cool family because of Debs.
Years later, when she started to go off the rails and give my long-suffering (and, by now, cancer-suffering) mother a hard time, I privately berated her for not being grateful for everything she'd been given. It didn't occur to me that the gift itself was the root of the problem.
Debs was not academic, but you had to run bloody fast to catch her on the race track. When she swapped basketball for Benson & Hedges as a lunch hour activity, she lost her only headstart. She got truancy off to a fine art, spending her lunch money on bus fares to Bristol where she would wander the city, befriending tramps, the homeless and anyone else who looked like they needed loving.
While I brought home a succession of spotty prefects, Debbie kept her love interests extremely quiet. She would suddenly start wearing a leather jacket I hadn't seen before, or I'd catch her sneaking a brand new Sony Walkman into her school backpack. I knew these were gifts from her "boyfriends" - invariably fat men over 50 who thought they might be on to something, but they got nothing more from her than a quick squeeze. She saw no moral difficulty in taking advantage of their foolishness.
In 1982, aged 17, she went to live in London as a nanny for friends, and within weeks, she had traced her natural family. It was the beginning of our lost decade. She moved in with her delighted grandmother and set about making herself more like them. She adopted patois, changed her appearance and reinvented her past. Her new friends drew her into the drugs culture of black London and for a while, I felt she had truly deserted me. I knew it for certain when I turned up at her flat one day and she was forced to introduce me as "Fraser's sister", referring to my white brother who also lived in London. It hurt.
But even in the rocky years, she came back when she needed me. I returned to my home in Weymouth late one night to find she had broken in and was smoking a spliff in my bed. She had an L-shaped cut on her throat where her Dominican boyfriend had threatened her with a knife when she said she was leaving. The two of us holed ourselves up for days, terrified he'd spot us if we wandered around the town. When I eventually had to go back to work as a reporter on the local paper, she came with me. That night, he was waiting outside the office. We held hands and ran like crazy through the narrow streets around the harbour, alternating between hysterical laughter and screaming fear. We've always been able to laugh.
Throughout our twenties, our lives became more and more incompatible and I accused her of throwing away her advantage. I know now it was nothing like an advantage at all, but at the time, I still wanted my mother to have been right. I didn't want her to die thinking she'd screwed up. I wanted to write a happy ending for all of us.
I'm more realistic about happy endings now, and I know too that she's by no means the only trans-racially adopted thirty-something still searching for herself. By the mid 1980s, these children were coming of age, catching sight of themselves sticking out from a sea of white faces on cine film or in the family photo album and wondering who the hell they were, and it was time for social workers to pick up the bill.
Debs put it very clearly herself only a few days ago. "You're always accusing me of living life in the fast lane," she told me, "but I don't live in the fast lane at all. I just stand around on the central reservation while the cars whizz past." Or, in the words of her (black) half-sister during one of their crazy fights in the first turbulent year of their reunion, "You scratch the black and there's white underneath."
Things have changed. In 1989, the Children Act ruled that families of a similar background should be sought wherever possible, and that due regard should always be given to a child's racial and cultural heritage.
Hindsight is a frustrating thing, but there's a kind of happy ending after all. In 1995, some close friends also went down the road of trans- racial adoption. We saw them all this Christmas and far from being the last taboo, the colour of this child's skin is as up for discussion as her favourite video. That's the way to do it.
As for us, Debs and I will just carry on laughing, talking and writing the book.
'Katherine's Wheel', Rebecca Gregson's first novel, is published by Simon & Schuster this month as a paperback original, price pounds 6.99.Reuse content