For three months in summer back when I was eight years old, I had a little brother.

My childhood is fuzzy. The memories are hard to reach for, but happy ones are few and far between. When I think about Mom and Dad I remember their arguments about me. I made them worry a lot and there was always some new problem to deal with. Sometimes I wondered if they could both be happy without something going horribly wrong.

My brother could keep them happy. Even with everything else he did to them, I still think my parents would consider those three months the happiest days of their lives. If they could remember them, at least.

Mom brought him home one caliginous night, as the word-a-day calendar from her office would say. I don't know which poor child it ate back then to worm its way into her heart, but that was all it took. It was slow earlier on, though, so she tried to make me feel included at first.

"It's just for a few days," she told me as she fussed over him. "I just couldn't leave him out there. You can share your room while your father and I look for his parents. I can't imagine how worried they must be..."

She was untangling his matted hair with a fine comb. She had never been that gentle with me. Whenever I shrieked in pain, she would only tell me that it was because I never combed my hair.

"And if we can't find them," she continued, "we can go to the police-"

The boy stiffened under her touch, eyes wide. Then he screamed. I waited for her soft look to harden, for the cold order to go to his room. But she hugged him tight even as he thrashed and wailed.

"No, of course we won't go to the police," she murmured. "You've done nothing wrong. You're safe here. We'll give you everything you need."

I clenched my fists.

My parents printed posters and talked about reaching out to people they knew. But days became weeks and eventually I found the rolled-up posters in the trash. They never even tried to put them up. As far as they were concerned, I had a new brother now.

But Victor wasn't like us. He never slept. No matter how much Mom fed and bathed and cleaned him, he was always the same starving wretch covered in filth she'd brought home that day. He never talked, and I would have understood because I didn't like speaking either, but he never tried anything to make himself understood. He just stared silently, almost balefully, until my parents' frantic guessing game hit their mark. I wondered where he was raised, if he really had been born in a barn like my dad used to tell me occasionally. He thought nothing of standing over me while I slept. Knocking was a foreign concept to him.

I hated my new brother with every fiber of my being, but nobody else cared or noticed. They loved him. They thought he was perfect.

He didn't have to go to school. After the first week, Mom was convinced he'd been through a hugely traumatic event and trying to put him through classes would only upset him. I would come home to my favorite cartoons blaring through the house while Mom slaved away in the kitchen trying to make something Victor wouldn't reject.

The day I learned about the cuckoo, I was glad he wasn't in school. We were learning about parasites in biology, and all anyone could think about was worms.

"What about the cuckoo?" our teacher said.

Cuckoos were brood parasites, she continued, outsourcing their offspring to other parents. I knew what Victor was now. When the time came for our annual beach vacation, I knew I had to act.

That day I pushed myself with a manic zeal. I swam further out than I had ever managed before. Victor followed, sullen and quietly miserable as always, but the thing behind him had to keep up its act.

There was a little alcove in the water, hidden behind an outcrop of rocks. I watched, holding my breath, as Victor failed to wail or scream like a real little brother would if his sibling disappeared. He simply settled down to wait. Like the matter was settled and he would be an only child from then on.

Then he smiled with teeth far too sharp and numerous to be human, and I hit him in the head with a rock.

I learned this back when I was eight: in the right situation, we are all capable of the most terrible crimes.

"I saw through you too," I whispered as I held him underwater for good measure. "We're all monsters."