I arrived home at five-thirty having cycled from my job in the city to my house, a terraced house in a pleasant tree lined street between Clapham and Balham. However in the middle of January on a cold wet Tuesday night it looked like any other London street, bleak, with people scurrying home from the buses and the tube station about half a mile away.

I started cycling to work the previous summer. At first it would take me forty minutes to cover the six miles or so but, as I got fitter, it took less time. I found it quicker and much more pleasant than the commute on the crowded tube trains. I found a route that kept me away from main roads, and changed into my dark suit, shirt and tie at the office. There were a few other cyclists in the company and we had taken over one of the disabled toilets as a changing room. We had no disabled staff on our floor and, being the boss, I sent out a memo condoning the use 'while there are no staff requiring the facility working on the tenth floor'. At fifty-four I was the oldest cyclist by a mile, it got me a few odd looks, but, once I started to look fitter, I caught a few admiring glances from the young female members of staff.

Anyway back to the story.

As I opened the gate into the small front garden, pushing my bike through, I spotted a figure hunched in the corner of the porch. As I approached the figure I realised it was a young woman and she was wet through. "At last," she said as she stood up, "I've lost my key."

"Sorry love," I said with a friendly smile. "You've got the wrong house."

"No I haven't," she replied, looking me straight in the eye. "67 Badminton Road, SW12, this is where I live."

"No, sorry, you don't live here," I said, still smiling. "I bought this house in 2005, and I've lived here ever since."

She stood there quite calmly and repeated, "I live here."

What was I to do? I opened the front door and the girl walked in. She paused in the hallway, pointed up the stairs and said, "That's my room, at the front."

Under the light I noticed that she had some bruises on her face and one eye was black, she had obviously taken a battering off someone. I wondered if this had affected her mind. I put her age at about thirty-five but it was hard to tell under the shabby wet clothes. Deciding that she wasn't a threat, I said, "Sit in the kitchen and take that wet coat off, I'll make us a mug of tea."

Under the coat she wore thin dress, totally unsuitable for winter, so I found her an old sweater out of the hall cupboard and put the kettle on. I made the tea, gave her the mug, and asked her again why she was here.

"I live here," was all she said. I asked what her name was and she replied, "Susan Holt."

The couple I had bought the house from were not called Holt, but they had only lived here 3 years, so I was at a loss.

After a few more attempts to convince Susan that she didn't live here, and failing to find out where she did live, I decided I had no option but to call the police. I left her in the kitchen and went upstairs to the boxroom that I used as a study. I told the police about my uninvited guest and they asked a few questions, I said she wasn't violent or threatening, just confused. They said they would send someone round but it may take a while as 'there wasn't any threat to life or property' and that if Susan became violent or dangerous to ring them again and they would send a response car round.

I went back down to find Susan had finished her tea. I asked if she was hungry, she said that she was so I decided to feed her while waiting for the police. During the week I live on ready meals so I put two ready-made stews in the microwave, it was fortunate that Marks & Spencers had them on a 'buy one get one free' offer when I did my shopping the previous day.

I then tried talking to her about other things and soon realised that she was quite intelligent and well read. We got into a discussion about the problems in the banking industry, a subject close to my heart since I worked for Nat West. I had already applied for voluntary severance and would take it if the terms were reasonable, with 34 years service I should get a good payout.

We sat talking for a while after we had eaten and she seemed perfectly normal until I again brought up the subject of where she lived, she was adamant that she lived here.

Two police officers, a man and a woman, arrived at about eight o'clock in a small patrol car. I took them through to the kitchen and explained the situation. They talked to Susan and she seemed completely rational but she was still convinced she lived here. They asked her about her bruises but she just sat there as if she hadn't heard. They asked me if I knew how she got the bruises and black eye and I said "I have no idea".

The WPC sat with Susan and the PC indicated he wanted to speak to me alone in the front room. I convinced him that the house was mine by showing him a variety of bills and other documents bearing my name and the address. Then he rang his station and, after speaking to someone for a few minutes, went into the kitchen and said, "Come on Susan, lets get you home."

Susan looked glum but got up and went out with the PC's. Once Susan was in the back of the patrol car the PC came back to me and said "I'm at a loss but we'll take her back to the station and try to sort it out there. You've been decent, some folks would kick up a right stink, so good night sir." He gave me a wave as he got in the drivers seat and drove off.

I spent the rest of the evening watching TV. I went to bed and mulled it over for a while and was still of the opinion that the beating she'd taken had affected her mind in some way.

Wednesday night was cold and clear, and I arrived back just after five-thirty as I always did. There was Susan sitting in the porch. I thought of the movie 'Groundhog Day'. "Hello Susan," I said cheerfully. "What are you doing here?"

"I told you," she replied tersely, "I live here. Those people at the police station wouldn't believe me but they let me go this morning so I walked back here."

I wondered why the hell I paid taxes, considering the state of mental health care these days, but I was at loss to know what to do. I asked her in and we had a rerun of yesterday though I decided that calling the police again was a waste of time. We talked while I was cooking tea - after raiding the freezer - and, on most topics, I got intelligent conversation. We shared a love of the countryside, eighties and nineties music and we both listened to Radio 2. I asked her how old she was, she told me she was twenty-nine and her birthday was on the twenty-eighth of May. When I asked about a husband or boyfriends she just sat there without answering. I guessed it was a touchy subject.

I then had an idea. Two doors down there was an old couple who had lived there for 40 years or more, maybe they would know her or her parents. I went down to see them and explained what had happened. They told me a young woman called Susan Crawford had been living here with her parents during the nineties and agreed to come back with me. As soon as they walked into the living room they recognised Susan, and she recognised them. Ada started talking with Susan while I took William into the kitchen. He told me the Crawfords lived here until about 1999, and when Susan got married they moved away. He thought they had gone to East Anglia. We were piecing things together.

We returned to the living room where Susan was telling Ada that her parents had died a couple of years ago. Damn, if it's true, and I thought it was, no hope there, Ada had already told me that Susan was an only child. "Let's have a cup of tea, Peter," said Ada, getting up from her chair, "come and show me where things are."

I knew Ada wanted to talk to me but she waited until we were in the kitchen. "She's been beaten badly by her husband. We didn't really know him but I know her parents didn't like him and didn't want her to marry him. They wanted her to move to Cromer with them when her dad retired. Anyway, I have a suggestion, let her stay here for a few days, she can't go back to her husband. Mentally she is fragile but we'll keep an eye on her and find out if she has any other family who will take her in."

"Will she be OK here?"

"If you mean will she steal or do damage, I think I can promise that she wont. I knew her from a baby and a nicer girl I have yet to meet. We'll keep an eye on her over the weekend when you go to Sussex." She then busied herself with the mugs and milk, adding. "It's quite good fun really, we get bored these days. It'll gives us a mission, to help her get back on her feet."

"Surely it'll be too much for you, you're not as young as you were."

Ada chuckled and said, "I may be eighty-two and Will is eighty-four but we still walk two miles with the dog everyday. We're fitter than some of you young ones." As far as Ada was concerned, that was that and I didn't argue.

We went back to the living room and I told Susan she could use the front bedroom for the time being. Her face lit up and she seemed to look better straight away.

Ada found a few cast-offs and said she would take Susan out shopping tomorrow. I asked about money and Ada said, "It's OK we aren't paupers you know."

"I know, anyway I'll chip in £100 to help."

"OK that fair, if we match it we should be able fit Susan out with the basic if we're careful."

I sorted out a spare key and left the three of them talking while I got ready for the morning. Ada and Will left around ten o'clock, Susan went to the front bedroom and made herself at home. I heard the TV for a while and then dropped off to sleep.

The following morning I got up at seven as usual and washed and shaved. When I got downstairs there was a cup of tea and some buttered toast waiting for me. Susan was wearing an old dressing gown, no doubt donated by Ada. I set off to work at eight as always.

When I got home that evening and opened the front door I could smell cooking. Susan appeared at the kitchen door and said, "Dinner will be half an hour, time to wash and change." I always like to shower when I get in after cycling.

After a quick shower I chatted to Susan while she dished up a nice meal, steak pie, potatoes and vegetables. I got stuck in, I could get used to this. "Ada and Will took me shopping," she said as we ate. "I've got all the basic clothes I'll need for the time being. I also bought some fresh food for dinner. This is better for you than that prepared stuff." I wondered if this was her or Ada speaking but I was happy either way.

Ada and Will called by around seven-thirty and told me about the day. They hadn't had any success in tracing any close relatives. "And we know how to use the internet you know," Will added with a laugh. They seemed to have things under control.

Susan and I sat in the living room chatting. She told me how the house, unlike all the others in the street, had a large cellar. The cellar had been built as a bomb shelter by her grandad during the second world war. He told Susan the walls were re-enforced with old railway lines and were two feet thick. Apparently, he only got it finished properly as the war was drawing to an end. What the hell he did with all the clay and rubbish he excavated I don't know. But it was fun talking to someone who knew the history, even if it was secondhand.

We went bed at ten-thirty and Susan seemed quite relaxed. I heard the TV in the spare room.

On Fridays I always went straight to my house in Sussex, in the village of Eartham, near Barnham, and stayed there for the weekend. I intended to retire there. I rang Ada every few hours on Saturday until she got annoyed and said, "Look Susan is fine, she may be down on her luck, but she's capable of living a full and independent life so stop worrying." I decided to ring Susan on Saturday night and we chatted away, she sounded fine.

Monday night, I returned to my London home and another cooked Dinner. Ada looked in during the evening and took me to task for panicking when I was away.

Over the next few days we settled into a routine. Susan would have a meal ready when I got in and seemed to be quite happy. I gave her the money I used to spend on food plus a bit more and she seemed to be doing quite well with it. I noticed she had started a 'housekeeping book' and was accounting for every penny. I told her she didn't need to, but she carried on anyway.

Now that she had settled down and the bruising of her face had gone down I began to see the real Susan. She was medium height and had a nice figure, not skinny or fat, and long brown hair which she kept in a scrunchy during the day. She had an attractive face and a nice smile. I asked her if she wanted to go out either with me or on her own in an evening, but she said no, it was nice to be at home where she felt comfortable. Ada told me she went out during the day on her own and did the shopping etc.

Susan asked about my wife one evening and I told her she had died suddenly at the age of forty-eight, two years ago. She asked if I still missed her, and I said I did and that was why I sold our big house near Wandsworth Common. I didn't want a London house, I would have commuted from Sussex every day, but at the time my two boys who were now in there late twenties still wanted a London 'crash pad' as they called it. But they were both now living abroad, Steven was in Australia, and married an Aussie girl last year, Richard was in Canada with his wife of five years, and I thought they would be unlikely to return to the UK permanently. I visited them both every year.

We sat down with Ada and Will about two weeks later and they said they had not been able to trace any relatives. I suggested that Susan remain here, I would pay her a small salary and provide board and lodgings in return for the housekeeping tasks which she had been doing willingly for nothing. Susan agreed immediately so the arrangement became permanent. I asked again about her husband, but was told by Ada, "He's a nasty man, a bully and a wife beater. She wont contact him and I don't blame her at all." I wondered if he would try to trace Susan, but kept my thoughts to myself. I did however make sure that the door bolts and chain worked and were secure. I also fitted a spyhole to the front door so that you could see who was there before opening it.

My misgivings about her ex-husband were confirmed the following week when I got home. I could tell Susan had been crying. I asked her what was the matter and she told me Johnny had been round threatening her. She had the sense not to open the door but he had banged on the door and windows and said he was going to hurt her.

I rang Will, he confirmed her story and said that the second time he and Ada came down in time to see him running off. I said that he needed stopping and Will said something which surprised me, "A big lad like you should be able to teach him a lesson." I thought about it and a plan formed in my mind. It was twisted and illegal but I decided I stood a good chance of pulling it off. I was that incensed with his behaviour I didn't care. I suppose I was protective of Susan, after all. my life had improved since her arrival, I liked having her around.

In spite of the upset, Susan had cooked a nice dinner and, while we were eating, I floated an idea. "If you could get your own back on your ex-husband for beating you all these years what would you do?"

As expected, she said nothing but I noticed her eyes flash; she wanted revenge, of that I was certain. I asked again and added, "Don't worry about it being strictly legal."

"I'd beat him until he screamed like I did," she said, her face taut. "Then I'd let him know how it feels to have something rammed up his arse."

Hell, her reaction shook me and I realised that he used to abuse her sexually as well. Well, I was on a roll so I continued, "If I set this up would you go through with it, and would it help you to get over it?"

"I've thought about how to get revenge for the last nine years," she said after a moments thought. "I'm a wimp at heart but if I had him helpless I'd beat him senseless." After another short pause she looked up and said, "What do you have in mind?"

"I think I could lure him here, lock him in the cellar, and give him some re-education."

"You'd do that for me even although you might get into trouble?" she asked, clearly surprised.

"Yes, and I think we'd get away with it. It'd be his word against ours so long as we stick to our story. Even if he went to the police there wouldn't be any evidence or witnesses. They may suspect what had gone on, but there would be no proof that we did it. I plan on scaring him into keeping quiet so I don't think it will matter."