The second she was fully inside the room, I slammed the door shut and frantically jammed the key into the lock. She was back at the door immediately, the ruse blown, twisting and turning the doorknob, screaming and cursing – but the job was already done. I had locked the door. She was trapped. Her fists continued to pound against the door. I stumbled backwards and turned around, unable to believe what I’d just done yet able to keep moving.

‘Come on!’ I yelled at Emma, who poked her terrified face out of my bedroom door, shaking her head.

‘I don’t want to!’ she cried.

I grabbed her hand. ‘You have to. Remember your promise?’

She hesitated then nodded and I tugged her out of my bedroom, across the landing to the stairs. Mother’s screams were crazed, her rage terrifying. Her fists pounded and bashed the door with so much force I feared she was going to break it down.

‘Run!’ I shouted, pulling Emma down the stairs.

We reached the second last step and stopped. Patrick stood at the bottom of the stairs looking concerned. In that moment, he looked huge and almost as terrifying as Mother.

‘Hey, hey, hey! Slow down, girls. What’s going on?’ he said, holding up his hands.

I sucked in a quick breath, knowing I had to get this right, hoping he was a good person. ‘Please help us. She’s not our—’

Mother’s voice cut across mine, drowning me out, ‘DON’T LET THEM OUTSIDE, PATRICK! THEY’RE ALLERGIC TO THE LIGHT! THEY’LL DIE!’

Patrick sighed. ‘Girls, what’s going on?’ He crouched down at the foot of the stairs and smiled sympathetically.

I pulled Emma close to my side and tried to sound as mature and clear as I could. ‘You have to find a way to get us out of here. We need to leave. She’s not our real mother. She’s—’

‘Now, now, slow down there, girl. You’re scaring your little sis.’ He reached out to pat my arm but I jerked back out of his reach. His eyebrows shot upwards and he chuckled and shook his head.

‘Look, I get it. You have this horrid, rare disorder and it must be mad awful having to stay cooped up inside here all the time, but it’s not your mother’s fault. She has to keep you inside. It’s her job to protect you.’

I tried to stay calm, tried to ignore Mother’s ranting from above us. ‘Please, you have to believe me. She’s not our mother. She took me from my parents ten years ago. My real name’s Polly Dalton. And she took Emma from her parents not that long ago. Surely you heard about a missing girl? It must have been in the newspaper.’

He looked like he hadn’t heard me. His eyes were on the ceiling, his attention on Mother’s words, not mine.