Left by himself, Rodney looked around him properly for the first time. The medical equipment around him looked standard as far as his limited medical knowledge could tell, but the walls looked strange. He couldn't describe it, but somehow they did not look how he would have expected hospital walls to look like. He was in one bed in a row of beds, all made up with lime-green sheets and blankets, but the others were all empty and the one nurse bustling around did not appear very busy. This was very different to the hospital Rodney had been in, which had been crowded and noisy with people constantly moving round him and talking and wheeling heavy equipment around.

The three people came back and Rodney watched their approach with interest. They did not seem to know how to treat him or what to say to him. The doctor checked the equipment monitoring him. "Well, I think you'll be fine," he declared.

Elizabeth looked closely at Rodney. "You're really twelve years old?" she asked.

Rodney nodded, suddenly feeling very uncertain. He put his hand up to his head, to feel where it hurt, then stopped and stared at his hand instead. It looked different. It looked – like an adult's hand, not like a child's hand at all.

John sat down by his bed. "Rodney." He sounded very serious. "Something's happened to you. There's been a bit of a mix-up. You're going to find this very hard to believe, but someone – I can't explain who right now – managed to pull your consciousness here into another body."

"Oh, good story." Rodney laughed, then stopped and stared in disbelief. "You're not joking about this, are you?"

"No, I'm not. Carson, have you got a mirror?" John turned to the doctor, who nodded and went away. He returned a moment later with a small hand mirror. John held the mirror out to Rodney, who took it gingerly and held it so he could see himself. He recoiled, letting the mirror drop onto the bed, then picked it up and stared into it again.

"How?" he whispered.

"It's a long story." John looked at Elizabeth, who took over.

"Don't worry, Rodney. We'll be putting our best scientists to work. They'll figure out how it happened and how to fix it."

"But who did this?" Rodney demanded, finding his voice.

The adults looked at each other. Eventually John spoke. "The person whose body you're in right now. Our chief scientist. Dr Rodney McKay. And we're not sure where he's gone, but we think he might be in your body right now. It's the only explanation we can think of."

Rodney stared, wide-eyed, then stared into the mirror again. It was weird. He thought of photos he'd seen of himself as a baby, how he could always recognise himself at any age. This was the same, but in reverse. This was knowing how he looked when young, but seeing a photo of himself as grown up, as old. He shook his head in disbelief. "This isn't possible," he said at last. "Now I know I'm dreaming."

The adults seemed to look a little relieved, if anything. "Aye, that's right, Rodney," said the doctor – Carson, Rodney remembered – "It's all a big dream and we're figments of your imagination."

"Some imagination," Rodney murmured, closing his eyes.

McKay stared up at his sister. It was difficult to comprehend, that this was his big sister, staring down at him. "I bet you're surprised to see me," he said.

"What?" Jeannie stood back from the bed and glared at him, frowning. "What are you talking about, Rodney? Listen, Dad will be back from work soon. He'll kill you if he finds you lying on the bed sleeping instead of doing your science project."

McKay frowned. Something was definitely wrong here. Could she not see the difference? A sudden thought struck him. He swung his legs off the bed and sat up. He could see his familiar childhood bedroom. He stood up and walked across to the mirror that hung over the chest of drawers on the back wall. He hardly dared look into it. Finally he raised his eyes to meet those of his reflection. Wide-eyed, he put his hands up to his face, feeling his smooth babysoft cheeks. A mop of unruly hair stood up from his head, tousled from his sleep, while his eyes looked swollen and red from crying. He shook his head in disbelief, then turned to face his sister.

"Jeannie, I need to tell you something," he said, but she interrupted before he could say more.

"I got a place, Rodney! I got a place! I'm going to college next semester. I'll be in the student block to start with, but I'll have to find my own place. Maybe I'll find some friends to share with. Oh, it's going to be so much fun!"

She stopped, seeing the expression on his face. "It won't be that bad, Rodney," she reassured him. "I won't be that far away, and I'll call regularly, and if I get a place of my own perhaps you can come to stay. If you learn to do what Dad tells you, you'll get along fine."

"No, you don't understand," said McKay desperately. "I'm not who you think I am, I –" His words were interrupted by the slamming of a door downstairs. "He's back."

He stared at Jeannie, wondering desperately what to do. He had been surprised at the reaction he'd felt in his body when he heard that door slam, that unconscious tensing of the muscles, the instinctive reaction he felt as his heart rate increased.

"You'd better look busy," warned Jeannie. But before McKay could do anything the door to his bedroom opened.

"Rodney?" His father stood framed in the doorway.

"Yes, sir?" McKay swallowed hard. He did not need to be afraid of this man. Not any more! But he could not fight the instinct to submit, to feel fear and withdraw from battle.

"Is your project finished?"

"I…" McKay was unsure how to answer. His father looked on the desk that was strewn with papers, and obviously saw his own answer there.

"There'll be no dinner for you tonight until that bloody project is finished. I've had enough of this, Rodney. You will knuckle down and get your school work done or I will make your life a misery."

"You already did that," McKay found himself muttering.

His father stared at him, shocked. "What did you say?" he demanded.

"Uh, nothing, sir, sorry. I'll get on with it now." McKay desperately fought for thinking time. Science project. What did he remember about a science project? He suddenly realised what was meant. "Oh, yes, science project. Yes, no problem." He found himself babbling and fought for control. He would not disintegrate before this man!

His father nodded curtly and turned away, before turning back to add, "and Jeannie, I'm sure you have work you're meant to be doing too."

"Yes, Dad," she answered demurely. "I'm just about to get on to it. My teacher liked that last essay I submitted. Did I tell you I got an A?"

Her father just grunted and left the room, leaving McKay feeling weak at the knees and Jeannie grinning at him. "Why don't you just do as you're told?" she asked him. "Your life would be a lot easier."

"I know," McKay answered soberly. "I don't know why I wouldn't do it, except that it always felt like giving in. The more he pushed, the less I wanted to do it. And as long as I was running away from medicine instead of towards science…" he stopped as he saw the blank look on his sister's face. "I don't know," he said again.