‘Take Z,’ I said. ‘Then go quickly. Remember, head down, run and don’t stop for anyone. Get to the park and wait for my call.’

Aiden took the dog, cradled him in his arms. I thought for a moment he was going to say something, maybe come over and give me a hug.

‘Go now,’ I said.

And Aiden turned, opened the door and was gone. As soon as he left I twisted onto my side, facing away from the door, and pulled the covers over me. I hadn’t rescued Aiden yet. If Mum discovered the swap soon, she would reprogram the car to stop before it got out of the clinic’s grounds. I had to buy Aiden time – at least five minutes, more if I could manage it. Every second counted. And that meant I mustn’t say anything when my parents came into the room. It’s possible they would think I was Aiden just by appearance – we are identical – but my voice would definitely give the game away.

Thirty seconds went past and then I heard the door close, footsteps approaching the bed. I couldn’t pretend to be asleep. No one would believe that within seconds of my sibling leaving, I’d drop off. The only option I could think of was to fake being upset. So I made my shoulders heave a little, as if I was sobbing but trying to keep it under control.

‘Aiden?’ Mum’s voice. I didn’t respond. She put a hand on my shoulder, but I jerked away from it. If it seemed I was angry and upset with her, it would explain why I wasn’t speaking. But I could only do this for so long. I checked my mental clock. Just under a minute. Aiden would probably be leaving the building about now, looking around for the car.

‘Aiden. What’s the matter?’

I brought my right arm out from under the bedclothes and waved it at her – a ‘go away’ gesture. I really wanted to turn to check if Dad was with her. Maybe my instructions had been ignored. Maybe Dad had followed his apparently distraught daughter to the car to offer comfort. That would mean disaster.

‘What’s the problem, son?’ Dad’s voice. I breathed a little easier. Just over a minute. He should be in the car by now. Another minute and he’d be through the gates. I didn’t say anything, just drew the clothes tighter around me and moved towards the edge of the bed as if trying to get further away from their voices.

‘Has Ashleigh been talking to you?’

I risked it this time. I turned and dipped the bedsheet to just below my nose. I guessed my eyes must be red, but I screwed them up anyway. I nodded and then turned away again.

‘What has she told you? Aiden, what did she say?’