It was late one Saturday night and I was alone at home doing some painting and decorating. I had decided to let my place for the year as I was going off to college. This was the last chance I had to give it a fresh coat of paint. At about 2am the doorbell went.

I was three storeys up, so I went to the window and looked out. A young black woman was standing on my doorstep. She had a white shawl wrapped around her shoulders and seemed distressed. When I asked her what was wrong, she explained that she was pregnant and had been beaten up by her boyfriend. She wanted to use my phone. My sympathy went out to her immediately, and without a moment's hesitation I went downstairs to let her in.

Once inside she asked to use the loo first, not the phone. I showed her where it was and she disappeared for some time. When she emerged, she sat down where I was painting and asked for a cigarette. She smoked it nervously and continued to tell me about her boyfriend and what a terrible row they'd just had. She seemed very agitated and kept pacing around the flat. She kept looking around a lot, too, making sure to keep well away from the windows. I thought this was because she didn't want to be spotted from the street by her boyfriend. She garbled on and on for quite a while, repeating her story, which became more confused each time, and becoming more and more distressed. At this point it started to dawn on me that I might have a hard time getting her to leave.

Finally, she used the phone to call her mother. She said the number was engaged, however, and would try later. She wanted another cigarette and an ashtray and went off to find one. As the house was empty, I didn't think I needed to keep an eye on her. She was gone some time, and when she returned she changed her whole story. For some reason she now wanted to go to Brixton - not her mother's. For the first time alarm bells started to ring. I knew something dodgy was going on and just wanted to get rid of her, so I told her to ring my local cab company and order one, at my expense. I gave her pounds 20 and made a point of watching her leave.

Upstairs I started painting again, a bit flustered and confused by my visitor. I knew she'd been trying to con me and was glad she was gone. But something still didn't feel right. I felt uneasy. I just had to go downstairs one more time to check on things. Paint pot still in hand, I went down to the landing, which has some stairs leading straight to the front door. For one long silent minute I just stood there, staring at my front door. Then there was a loud bang.

The door flew open and a man wearing a balaclava rushed at me from nowhere, screaming and shouting. I stood rooted to the spot in terror. The paint pot slipped from my hands and rolled down the stairs spilling paint everywhere. He tripped over it, but in seconds had regained his balance and was on me, slashing the air with a sharp-looking knife. He made no threats and gave no warning. He just tore at me, stabbing the air with his knife. I threw my arms up to protect myself and, to my horror, felt the cold steel plunge into my forearm. If I hadn't put my arms up, the knife would have gone into my face or chest.

After this initial attack, it was all I could do to keep my body as far away as possible from his slashing knife. Luckily, I was strong enough to hold him at arm's length. Nevertheless, my chest and torso were being nicked by the tip of his blade, and by then the wound on my arm was beginning to bleed badly.

We struggled on the stairs for what seemed a long time. I managed to get my wallet out of my back pocket and tossed it down the stairs. He stopped attacking me immediately and dived after it. Then he tore off through the door, leaving a trail of white footprints behind him. I ran to the door - to see an unmarked police car screech to a halt in front of me. It was all too bizarre. They seemed to know exactly what was going on and I was stunned to see them. They explained that the cab driver had tipped them off.

When the woman had got into the cab, she had been joined by her so-called boyfriend. He had demanded money from her, and when she explained that she hadn't managed to get any, he became violent and had drawn a knife. He instructed her to wait in the cab and leapt out, saying he was going back to my house to get some money. The cab driver, however, had no intention of waiting around. The minute the man got out, he threw the woman out, too, and sped off - straight into the unmarked police car. This had all taken place while I was being attacked.

The police administered some emergency first aid to my arm before piling me into their car to search for the man. We drove around the area for some time, but had no luck, despite the trail of white footprints. Back at my flat we found that the woman had left my door on the latch. I'd been set up. I also found that she had rifled through all the cupboards and drawers in other rooms, but obviously had found nothing. This was why she suddenly changed her story. I'd been a disappointing set up, and she wanted to get away from the man she had to report back to. The police also pressed the redial button on the phone to try to trace her call, but the number she had dialled didn't exist. She was a seasoned confidence trickster and was well known to police in the area. I found out later that the night after my attack, she had robbed another man in the same way, with the same story.

Now I know I will never let anyone into my home again, no matter how distressed or in need of help they seem. At the time I had believed the woman's story and wanted to help. It never occurred to me to be wary or mistrustful. It's sad that a genuine act of kindness was abused, for it won't be repeated.

The woman has since been arrested for aggravated burglary and is awaiting trial. She has 11 other charges pending for gaining entry to premises in the same way. The man has not been caught.