"Through me, Cara's ghost came to life": the author with her twin sister Cara shortly before she died in 2006.

"Through me, Cara's ghost came to life": the author with her twin sister Cara shortly before she died in 2006. Photo: Supplied

We used to be identical twins. Born in July 1978, Cara and I had the same thick dark hair, angular faces and knobbly knees. I was slightly thinner than Cara and my feet were a size bigger, but we both had slightly crooked canine teeth and bitten-down fingernails.

We were our mother's only children. She called us her ladies. Other people called us "the girls". Cara called me Her. Ours was a middle-class upbringing. As children, we played hide and seek under a weeping willow in our garden, carving our names in its trunk with a rock.

We were just 28 when Cara died after her life plunged into a spiral of depression and self-destructive behaviour. In the months before she died, we'd fallen out. The last time I saw her, I told her, "I'm not going to have anything more to do with you until you sort yourself out." Only three weeks later, my twin sister was dead.

I forgot who I was after Cara died. The power of her memory was so strong, I'd see her instead of me. I gazed at myself in the mirror and there she was, her rusty brown eyes, frightened and curious as a doe's. I'd smile at myself and see her grinning back. Her square waist, narrow hips and round breasts were now mine.

I learned later that this heartbreaking delusion - that you are looking at your dead twin when really you are looking at yourself - is a common experience among identical twins when one dies. The surviving twin finds it impossible to differentiate their living body from that of their dead twin. They become a breathing memorial for their lost half.

Certainly, I found myself mimicking Cara's self-destruction to try to bring her back. I missed her so terribly I tried to tear apart my life, just as she had. I felt that by doing so I'd be nearer to her.

In October 2001, when she was 23, something terrible happened to my sister, something that beat the hope and wonder out of her and ultimately led to her death. She was raped in the woods near where she lived in Massachusetts while she was out walking her dog. At that moment, my sister and I were untwinned: our bodies were the same, but Cara became lost in hers. A broken twin hates you for reminding her of what she once was. You, in turn, fear her for showing you what you could become.

Cara limped along after the rape. She studied for a degree, but I had the feeling that her passing it was an act of mercy on the part of her professors. But then Cara began to disappear a couple of evenings a week. I'm not sure when she started to use drugs but I convinced myself there was no hiding her problem from me.

Twins love each other but they also bicker, fight and judge. All the things a twin hates about herself are obvious in the other. Because I knew her so well, I could see Cara was high as soon as she walked into a room. Yet even that knowledge and understanding couldn't save her. She overdosed on June 13, 2006, almost five years after the attack.

At Cara's funeral I stood at her casket and received her mourners. Red roses arranged in the word "sister" were on an easel behind me and stood as high as my head. Mum had bought them on my behalf. Some people, ignoring Cara's body, approached me instead. They saw in us the same person: one dead, one half-living. Through me, Cara's ghost came to life. If she hadn't already died, I'd have killed her for putting me through that.

I was the last person to see my sister before we closed the lid of her coffin. I knelt down beside her and wept. My tears fell on her face and made lines in her make-up. I felt as though she was alive in me, with all of her troubles.

After Cara died I stopped eating. I didn't want to look like her any more. I looked at myself in the mirror and pulled at the tiny roll of fat on my stomach. I began to starve Cara away. I felt I had to rid myself of her likeness to travel back to myself.

For the time being, I kept my job teaching photography at a college, but I was exhausted by my grief. I dressed mainly in Cara's clothes and wore them down to rags.

I was convinced I could talk to Cara, and that she was asking me to become her, to give her life and to join her in death. So I got ready to die. I swallowed prescription pills. I refused sleep out of fear of dreaming of Cara. I lived alone in a house I filled with my sister's furniture, and I gave up my job. I tried to chase my sister into the afterlife.

I also read that 50 per cent of bereaved twins die within two years. That statistic did not discriminate between disease, suicide or accident. Flip a coin: those were my chances of survival.

I missed Cara continuously. I couldn't get through a day without medication. My doctor prescribed pills to help me sleep and allay my anxieties. They worked: I didn't walk in front of a bus, though I wanted to. I saw psychiatrists, too, but it was my friend Grace who really helped. We'd met years before, but had become closer after her sister and mother died within months of each other. We found an enormous kind of relief in one another.

Then, in 2010, Grace introduced me to Tony. We'd both been raised by strict military fathers and had suffered the loss of a sibling in our late 20s. Tony grieved for Jeff, his older brother, who lost a battle with non-Hodgkin's lymphoma.

He told me he had Jeff's ashes in an urn on his desk. There was no place he'd found that had been right to scatter them. I'd met him just in time, Tony said. He'd travelled the world and was exhausted and running out of money and hope. I'd heard of love at first sight, and thought the idea ridiculous. But as I sat with Tony and observed his kindness, I wasn't so sure any more.

The first night I spent with him was the last night I took one of the pills I'd previously been so dependent upon. He cooked me a delicious dinner and I felt something unexpected: hope. Tony wasn't the cure, but his love helped heal my hurt. We were married three months later. I realised I had been given the gift of life and resolved to hold on to it as tightly as I could.

During our honeymoon, I became pregnant with our daughter Josephine. The pregnancy was straightforward but I worried that Josephine would look like Cara.

When my labour began, it was Cara I called for. I closed my eyes. A woman stood with her back to me and I recognised her as Cara as she turned to greet me. She held her hands on her hips and smiled with half of her mouth.

Cara stood at one of my shoulders and Tony was at the other. She looked into my eyes as I pushed and smiled, as if she was giving me her permission to live. At 5.22am, on September 16, 2011, Josephine was born into her father's loving hands. He carried her over to me and set her on my chest. She looked identical to no one, just exactly like herself.

Her: A Memoir by Christa Parravani is published by Henry Holt & Co.