I woke up suddenly, asleep to wide awake in seconds. Heart pounding.

What was it?

Stuart stirred beside me, one hand lifted, on my arm, pulling me gently back down. ‘Hey,’ he murmured. ‘Go back to sleep.’

‘I heard something,’ I said.

‘You were dreaming.’

He fitted an arm around my middle. I lay back down, still, my heart still hammering. It had been a noise again, like before. A bang.

Silence, just my heart, just Stuart’s breathing. Nothing else.

It was no good. There was no way I was going to go back to sleep.

I got out of bed, trying not to wake him up again, pulling on a T-shirt and a pair of shorts. Barefoot, I tiptoed out of the bedroom.

The flat was in darkness. I looked down towards the front door. It looked back at me, solid, silent, reassuring. The front room was bright, orange lights from the streetlights below illuminating the ceiling. I crouched down and sat on one of the low windowsills, looking down into the street.

It was utterly quiet, no movement, no cars. Not even a cat. The only sound was the distant drone of a plane, lights like stars flashing in the dark orange sky.

I was just thinking about going back to bed when I heard it again. A bang. A thump, dull, like something soft falling a long way.

It was in the house somewhere, downstairs. Somewhere below.

I thought about waking Stuart. My anxiety levels were high, somewhere around a seventy or eighty. My fingers were shaking and my knees were unsteady as I stood up. I waited for more. Nothing.

Fuck it, I couldn’t be doing this for the rest of my life. I was going to check.

I padded in my bare feet to the door and, after a moment’s hesitation, opened it. The stairway was dark, chilly, with a draught coming up from the floors below. I waited for my heart to stop thudding quite so hard. There’s nothing to worry about, I told myself. It’s just our house. It’s just Stuart and me, there’s nobody there. Go and have a look.

I went downstairs, leaving Stuart’s door open. There was light from the front door, below, and dull light from the window on the landing. Otherwise it was dark.

When I was outside the door to my flat I stopped and waited, listened. Nothing at all.

This was ridiculous.

I went downstairs, one step at a time, keeping to the edge so it didn’t creak. The draught was worse now, almost a breeze. It lifted the hair on the back of my neck. Dank air, stale air – the scent of cold soil. The smell of graveyard earth.

I could see the front door now, firmly shut. No sign that it had been opened.

Then, suddenly – BANG – close by.

Not loud, but certainly loud enough to make me jump. I crouched down so I could see through the banister to the door to Mrs Mackenzie’s flat.

The door was open again. Wide open.

Frozen to the spot, I looked into the inky blanket of blackness inside the flat. The noise I’d heard was like a cupboard door shutting. Echoing in the empty flat. Someone was inside.

Breathing as deeply and slowly as I could, I tried to concentrate, to think. This was crazy. There couldn’t be anyone in there. If they were, they were fumbling around in the dark. Why didn’t they just put a light on? I hugged my knees and waited for the panic to ease off. Of course it would have been easier and quicker to go back upstairs, to shout for Stuart, to go and start checking my own flat to make sure it was safe. But I’d come all the way down the stairs on my own and I wasn’t going to give up now.

‘Cathy?’

The voice behind me, right behind me, made me scream and jump. I screamed louder and harder than I’d thought possible.

‘Hey, it’s me, it’s okay – what on earth – ? Cathy, sorry, I didn’t mean to creep up on you.’

I was shaking from head to foot, pressing myself against the far wall. I pointed at the open door, the yawning, gaping blackness. ‘I heard – I heard…’

‘It’s okay. Come on, take some breaths.’

In addition to the panic I was furious.

‘What the fuck…?’ I said, when I could speak. ‘Why the hell didn’t you just say something? You just about gave me a fucking heart attack.’

He shrugged. ‘I thought you might be sleepwalking.’

‘I’ve never fucking sleepwalked in my entire life.’

‘Well, what are you doing, then?’

I looked at the doorway. If there was someone inside, we’d probably given whoever it was a fright. My scream alone must have woken up half the street.

‘I heard noises. I came to have a look. And – see – the door’s open. I bloody locked it. I locked it and I checked it. And now it’s open.’

He made a tutting noise, an ‘oh, no, here we go again’ noise, and moved me out of the way. He went to the ground floor and turned the light on. We both blinked and shielded our eyes from the sudden brightness. The doorway still stood, black and empty. I could see a few feet of crazily patterned carpet.

Stuart looked at me with a world-weary expression and stood in the doorway.

‘Hello?’ he shouted. ‘Anyone there?’

Nothing, not a sound. He went inside.

‘Be careful,’ I said.

The lights went on in the flat at few moments later. I crept down the stairs. Everything was suddenly less threatening with the lights on. Stuart was in Mrs Mackenzie’s living room, standing there next to the sofa in his boxers and bare feet. ‘There’s nobody here,’ he said. ‘See?’

I could still feel a draught. ‘Look,’ I said.

The bottom pane of glass in the kitchen door was broken, a wedge-shaped piece of glass about a foot wide smashed on the floor. Through it the smell of the garden, a night breeze, was breathing a chill onto the skin on my legs.

‘Don’t go closer,’ he said, ‘you might cut your feet.’ And then, ignoring his own advice, he went closer.

‘There’s fur on the glass at the top. Looks like that fox has been getting in.’

‘That bloody fox again,’ I said. ‘And do you think it used a hammer to smash the window?’

He stood up and crossed the kitchen floor to me, avoiding the broken glass. ‘There’s nobody here,’ he said. ‘Let’s go back upstairs.’

We shut the door, slammed it. Stuart wouldn’t let me check it. The latch had shot home, we’d both heard it. We went back upstairs and Stuart went back to bed. I sat in the kitchen with the lights on, drinking a cup of tea. My hands were still shaking, but even so I felt quite calm. I couldn’t believe I’d actually done it, gone down the stairs in the middle of the night, left the safe place, left Stuart’s bed, and gone out through the door and down the stairs.

Despite the broken pane of glass, despite the fact that Mrs Mackenzie’s flat had clearly been broken into – and not just by a fox or any other animal for that matter, it had to have been a person – I felt calm and free and composed.

And still angry. Not just that he’d sneaked up behind me, not just that he’d made me scream and so alerted whoever it was who’d been in the flat, but that he thought I’d done it. He thought that I’d opened the door to the flat. He wouldn’t say it, but I saw it in his eyes.

He was starting to doubt me, the same way Claire did, and Sylvia, and then the police, the judge, the doctors, everyone.

I didn’t go back to bed. I put the television on and stayed up until it got light, half-watching, half-practising thinking about Lee. I was already wired; it didn’t seem hard to take a step further and test my anxiety levels to the extreme.

I thought about him breaking into Mrs Mackenzie’s flat. I thought about him living down there, in the darkness, listening to Stuart and me in the flat upstairs, listening to us talking, listening to us making love. I thought about him and what he might be planning to do.

When it got light, finally, I had tears on my face. I wasn’t panicking; my breathing was steady. Controlling it, the panic, was definitely getting easier.

When I heard Stuart stirring I went to put the kettle on.

I took him in a cup of tea.

‘You alright?’ he said, his voice sleep-slurred.

‘I’m fine.’

‘I’m sorry,’ he said. ‘I’m sorry I scared you last night.’

‘It’s okay.’

‘I’ll ring the management company later, get them to send someone over and fix that broken glass. And put another lock on the door. Okay?’

‘Sure. I’m going to go down and get ready for work.’

He touched my arm. ‘Already? Come back to bed.’

‘It’s nearly seven. I’ll see you tonight, okay?’

I kissed him. He rolled over in bed for another five minutes’ sleep and I left him to it, heading down the stairs to my own flat. The urge to start checking everything was still there, but now I always restricted it. Instead of checking the windows and doors, checking the curtains were exactly as I’d left them, I checked other things.

If Stuart, or Alistair, or anyone else for that matter, had asked why I did it, why I checked, I would not have been able to explain. Nobody else would notice the things that I noticed, the little signs that Lee had been in here. The door was always locked, just as I’d left it, but that meant nothing. I couldn’t explain how I knew he’d been in here while I’d been away.

I just knew.