I took Friday afternoon off work for my first appointment with Alistair. I was expecting to be more nervous than I was. I waited upstairs at Leonie Hobbs House, thinking of Christmas Day.

The clinic was busier, several people waiting to be seen, although hopefully not all of them waiting to see Alistair. There were several clinic rooms and there was a steady traffic of people in and out. No sign of Deb and her lip-ring today; behind the clinic reception desk on the first floor was a comfortably built lady in her fifties with battleship-grey hair and an NHS badge attached to her navy cardigan proclaiming her name to be Jean.

She hadn’t spoken to me, other than to ask my name. She didn’t make eye contact with anyone in the waiting room, just kept a close watch on her computer screen and on the pen attached to the desk by a long, thin chain.

‘Cathy?’

I jumped to my feet and walked down the corridor to the only open door, through which Alistair must have run before I saw him.

‘Come in, come in. How are you, my dear? It’s good to see you again.’

With his effusive welcome I was half-expecting him to jump up and kiss my cheek, but fortunately for both of us, he didn’t. He was sitting on a leather armchair next to a second chair and a sofa. He looked well, smiling at me and indicating I should sit down.

I chose the chair. ‘Hello again,’ I said. ‘Did you make it home alright on Christmas Day?’

‘Oh, yes. I managed to get a cab just up the road, I was quite surprised to find one so easily. Marvellous chap. Thank you, I did have the most wonderful time. And it was lovely to meet you after hearing so many good things from Stuart.’

I was starting to feel a bit shaky.

‘Now, then,’ Alistair began. ‘I’ve been looking at your assessment. You saw Dr Parry, am I right?’

‘Yes.’

‘And he prescribed an SSRI for you?’

‘Yes.’

‘Good, good. And you’ve been taking that – let’s see – around three weeks?’

‘About that.’

‘They do take a while to kick in, sometimes. It might be a while before you see any effects.’

‘They’ve not made me feel spaced out, anyway. That’s what I was worried about.’

‘Hm, no, they’re not at all like the drugs you’ve had before, looking at your notes. Much more appropriate. Do you know, I really do feel you must have had an appalling time of it. The last time you were treated, I mean.’

I didn’t answer.

‘I shouldn’t comment, really, but – hm. Anyway. It seems to me, my dear, that you might have two issues here, existing side by side. Your assessment indicates that you’re clearly suffering from OCD, and the level of that is what we would call moderate-to-severe on the Yale-Brown Compulsive Symptoms checklist, the YBOCS list. Now Dr Parry noted, and I would tend to agree, that you also have plenty of symptoms which more resemble PTSD, that’s post-traumatic stress disorder. The symptoms for this can be similar to OCD in terms of stress, but include things such as flashbacks, nightmares, an exaggerated startle response, and panic attacks.’

He flipped over the pages in his notes. ‘And I think you’ve been suffering from all of those…’

‘Yes. I guess so.’

‘And would you say they’ve been getting worse?’

‘They get worse and better. I mean, I had a bit of a fright at the beginning of December. I had some bad panic attacks and nightmares for a week or two after that. And the OCD was worse, too. Then things got better for a while. Then Christmas Eve something else happened to set me off, and again, everything was a bit grim for a while. At the moment, it’s not too bad.’

Alistair was nodding, patting his expanse of a belly reverently as though it contained a baby rather than merely his dinner. ‘It’s that pernicious worm of doubt, isn’t it? You know full well that the door is locked, the tap is turned off, the switch is turned off, but still there is that doubt, and you have to go back and check again…’

He shuffled his papers and wrote a few lines of scribble on what looked like a dog-eared bit of scrap paper. ‘The good news is that the therapy we can provide will help you with both OCD and PTSD. You’ll need to be willing to work on this at home, on your own – and the more you’re prepared to work on it, the better the result is likely to be. There will probably be some setbacks along the way, but with a bit of time and effort you will be able to get better. Okay?’

I nodded.

‘Let’s start at the beginning. Can you tell me a bit about what you were like as a child?’

I told him, slowly at first, the whole sorry story – leading up to but never seeming to reach the moment when I met Lee, the moment when my precarious life veered off towards that cliff edge. That would come later.

I had an hour and a half for the first session, next week it would be an hour, and so on once a week unless I felt I needed more. I’d agreed to try out some things at home. I was going to do something called ‘exposure and response prevention’. Sensibly enough, this meant exposing myself to the perceived danger, and then waiting until the anxiety subsided, without performing any of the checks or rituals which would normally help to reduce the anxiety. Theoretically, the anxiety would reduce of its own accord. Rinse, repeat again and again and again.

I remained a little sceptical, but I promised to give it a go.

My phone rang when I was still about a mile away from home. The streets were quiet, just the after-school traffic. I was thinking about going for a run with what was left of the afternoon, although it was getting dark.

‘Hello?’

‘Hey, it’s me. How did you get on?’

‘Okay. It was fine. Is that what you do?’

‘Pretty much. Not much to it really, is there?’

‘I guess not, if you do it every day. I kept thinking it must be really dull, having to listen to all that.’

‘Not at all. Everyone’s different, don’t forget. Everyone travels to that difficult point from a different direction. What are you doing now?’

‘I was going to go home and check three times. Why?’

‘I’ll call you later, shall I? I’m just going to take Dad out to the garden centre. I just wanted to… let you know I was thinking of you.’

‘I’ll ring you, if you like. When I’ve finished the checks. Would that be okay?’

‘That would be great. I’ll keep the phone handy.’

I kept thinking of one of the things I’d talked about with Alistair. Theory A and Theory B – it was something for me to consider. Theory A: that if I somehow fail to check the flat properly, someone will break in. Not just someone. That Lee will break in, and that I will not realise he’s done it. That I am actually in real danger if I fail to check thoroughly. Theory B: that actually checking the door once is enough, and that checking it over and over again does not make it any more secure, and that the reason for checking is simply that I am just extremely worried about being in danger. The two theories are in opposition to each other, and they cannot both be true. The rational theory is, of course, Theory B: that what I am doing by repeatedly checking everything does not make me any safer than checking once.

Even if I accept that Theory B is possible, how can I be sure that it is the truth? The only way, according to Alistair, is to carry out some sort of scientific experiment to see which theory holds water and which one falls apart under scrutiny.

It’s all very obvious where this is going. I check less, nothing bad happens, ergo it’s a complete waste of bloody time checking everything over and over again and I should stop doing it forthwith.

I’m not an idiot – even I know it’s a waste of time. That doesn’t stop me doing it.

And the thing that worries me more than anything is that actually this ‘scientific testing’ fails to take into account that my fears aren’t based on some ridiculous invented danger at all.

They’re based on the fact that Lee is out there somewhere, looking for me.

Assuming he hasn’t found me already.