When I was ten years old, I discovered a secret my mother had been keeping. The reason this matter was so crucial was that what my mother was keeping was not her secret. It was my secret.

That night, my parents went out. They didn't go out very often, and when they did they sent me next door to sit in Mrs. Robb's kitchen. The house next door was exactly the same as ours, except that the layout was completely reversed, and the reverse made me feel extremely dizzy, so when it was my parents' turn to go out for the evening, I once again insisted that I was old enough and sensible enough to stay in the house unattended. I didn't hold out much hope, but this time my father agreed. My mother was also persuaded, the only condition being that Mrs. Robb would come to our house at half past eight to watch.

They left the house at seven, and I poured a glass of milk and sat on the sofa to drink it in celebration, feeling terrific. Margaret Lee, was old enough to be left alone in the house without a temporary babysitter. After drinking the milk, I suddenly felt very bored. How should I enjoy this freedom? I began to wander aimlessly, measuring the new frontiers of my freedom: the dining room, the living room, the downstairs bathroom. Everything was no different than usual. Somehow I remembered something I had feared as a child, and it had to do with the Big Bad Wolf and the Three Pigs. I will blow, blow, blow your house down! It blew down my parents' house effortlessly. The dim, drafty rooms were powerless to withstand the attack; one look from the Big Bad Wolf at them and the fragile, elegant furniture would crumble into a pile of matchsticks. Yes, that big bad wolf could bring down the entire house with just one whistle, and the three of us would instantly become his breakfast. I began to wish I was in a bookstore; being in a bookstore never frightened me. The Big Bad Wolf could blow all he wanted: all those books would make the walls twice as thick, and my father and I would be as safe as if we were in a fortress.

I go upstairs to the bathroom and look in the mirror. To see what I look like as a grown-up girl for reassurance. Head tilted to the left, then to the right, I examined myself from every angle, hoping to see a different person. But all I saw in the mirror was myself.

My own room gave me no hope either. I knew every inch of it, and it knew me like the back of its hand; we were uninteresting companions to each other. So I pushed open the door to the guest room. The ostensibly unadorned closet and uncovered dresser appear to allow you to freshen up in here, but you understand that the closet and drawers are empty inside. The tightly wrapped and flat sheets and blankets on the bed also invite annoyance. The thin pillows look lifeless. This room was always called the guest room, but we never had guests. It was where my mother slept.

I exited the room with mixed emotions and stood at the top of the stairs.

That was it. A bar mitzvah. Staying home alone. I was moving into the big kid category, and tomorrow I would be able to announce on the playground that I hadn't been to the babysitter last night. I stayed home alone. The other girls will be dumbfounded. I've been waiting for this day for a long time, and now that it's finally here, I don't know how to react. I had expected to be in the mood to automatically adapt to the experience, i.e. I would see for the first time what I was destined to become. I had expected the world to shed its childlike appearance that I had come to know so well, to reveal its secrets to me, to show its mature side. Yet, in my new state of independence, I felt younger than ever. What was wrong with me? Will I ever find the secret to growing up?

I pondered wildly whether or not to go to Mrs. Robb's house. Oh, no. There was a better place. I crawled under my father's bed.

The space between the floor and the bed frame had shrunk since I last hid there. A suitcase clung to one of my shoulders, and in the pitch blackness under the bed, it looked as gray as the day was long. The suitcase contained all of our summer gear: sunglasses, spare film, a bathing suit my mother never wore but never threw away. A cardboard box sat on the other side of my body. Fumbling with my fingers, I flipped open the wrinkled lid, slipped my hand inside, and searched. The tangled mass of Christmas tree ornament lights. The dress of the angel who decorated the tree is caked with dust. The last time I stayed under this bed, I believed in Santa Claus. Now, I don't believe anymore. Does this mean I've grown up a bit?

Crawling out from under the bed, I removed an old cookie jar. Half of the jar was exposed beyond the ruffled edge of the hanging fabric along the bed. I remembered the jar: it had been under the bed. Its lid was stamped with Scottish crags and firs, and it used to be so tightly closed that I couldn't open it. I casually tried to open the lid. My hands were bigger and stronger than they used to be, and it was a surprise to me how easily the lid was opened. The cookie jar contained my father's passport and an assortment of papers of various sizes. Forms, both printed and handwritten. Some were signed in places.

For me, I read what I see. I always do. I flicked through the papers. My parents' marriage certificate. Their birth certificates. My own birth certificate - yellowed paper with a red seal and my father's signature. I folded it carefully and placed it with the other forms I had already read, and then I began to read the next one. It was identical to my birth certificate. I was perplexed. Why would I have two birth certificates?

Then I saw the difference. Same father, same mother, same date of birth, same place of birth, but different names.

What was happening to me at that moment? My original thinking fell apart in an instant, and my mind reorganized itself like a kaleidoscope of unusual thoughts.

I have a twin sister.

I ignored the jumble of thoughts in my head and curiously unfolded another piece of paper.

A death certificate.

My twin sister is dead.

At this moment I knew what made me flawed.

Even though I was bewildered by this revelation, I was not surprised. Because I'd always had a feeling. The feeling that there was something around me - a feeling so familiar that it needed no words. The air to the right of my body was always a little different. As if there was a shadow of light. Something special that warbles unoccupied space. It was my pale chimera.

Hands pressed firmly on the right side of my body, head down, nose almost touching my shoulder. It's an old pose that I can't help but strike whenever I'm feeling pain, confusion, and reluctance. I was so familiar with it that I had never given it much thought in the past, and now my discovery revealed its significance. I was looking for my twin sister. She was supposed to be there. Next to me.

When I found those two pages, when the truth came out and all was quiet again, I thought to myself, exactly that. Loss. Sadness. Loneliness. There was always a feeling that separated me from others - it stayed with me - throughout my life, and I found the two birth certificates, and I understood what that feeling was. My sister.

A long time later, I heard the door to the kitchen downstairs open. Despite the tingling in my calves, I ran to the stairway and Mrs. Robb appeared at the bottom of the stairs.

Is everything all right, Margaret?

Yes.

Do you have everything you need?

Yes.

Well, come to my house if you need anything.

Okay.

Your mom and dad, they'll be back soon.

Mrs. Rob left.

I closed the door and left the bedroom after putting the papers back in the cookie jar and putting the jar back under the bed. Standing in front of the bathroom mirror, I was shocked to feel my eyes locked with another pair of eyes. My face tingled under her gaze. I could feel my bones under my skin.

Later, my parents walked up the doorstep.

I opened the door and my father gave me a hug at the top of the stairs.

Good job. High marks in every way, he said.

Mother looked pale and tired. Going out always caused her a headache.

Yes. Good girl, she said.

So, sweetie, how are you doing at home alone?

Good.

I knew it. He said. Then he couldn't help but open his arms again and give me a happy hug and a kiss on the forehead. It's time to sleep. Don't take too long reading.

I won't read for too long.

Afterward, I heard my parents making the preparations before going to bed: my father opened the medicine cabinet, found my mother's pills and poured a glass of water. You'll feel better after a good night's sleep, he said, as he always did. Then the door to the guest room closed. After a while, the bed in the other room creaked and I heard my father click off the light.

I learned about twins. A single cell that was supposed to turn into a single person becomes two identical people for some unexplainable reason.

I am one of the twins.

My twin sister died.

How does this matter affect me?

I hid under the blanket, my hand pressed firmly against the silver-pink crescent-shaped scar on my body. It was the shadow my sister had left behind. As if I were a muscle archaeologist, I scrutinized my body for its ancient history. I was cold as a corpse.

With the letter in my hand, I left the store and went upstairs to my apartment. The staircase narrows a little with every three book heights. As I walked, I turned off the light behind me and began to prepare to write a politely worded letter of rejection. I could tell Ms. Winter that I was not the kind of biographer she was looking for. I have no interest in contemporary literature. I had not read any of the books written by Ms. Winter. I feel at home in libraries and archives, and I have never interviewed any living writer in my life. I feel more comfortable with the dead; frankly, the living make me nervous.

Perhaps it wasn't necessary to include that last sentence in the letter.

I don't want to bother cooking a meal. A cup of cocoa will do.

As I warmed the milk, I looked out the window. The faces reflected in the window glass at night were so dark you could see the dark night sky through it. We were cheek to cheek through the cold glass. Had you seen us, you would have realized that had it not been for this wall of glass, there really would have been nothing to distinguish us.