To catch a child molester: One woman's amazing 'sting' on her abusive stepfather

My earliest memories are feelings – smell, and being cold and wet. It was often dark, but I remember the first time I was introduced to that white flashing light that kicks off in my head, my brain's way of saying that pain was coming. A woman – my mother – was holding me at her eye level by my hair. I can't put an age to it, but there was certainly a cot and dirty towelling nappies.

I was virtually blind and deaf for a while. Imagine looking through toilet-roll tubes and that's all I could see; the same was true for my hearing: unless you were in a certain range, I didn't know what was going on. It wasn't a condition from birth: I got my hearing and sight back when the doctor told my mother I shouldn't be beaten across the head.

My mother, Jennifer, hated me. I can't fathom it: she died before I got a grasp of who she was. I just know she was never really there. She was off with boyfriends, or playing bingo, and "shopping" was a daily routine. We couldn't go anywhere without her doing it, but she could never give it its real name – stealing. I'd either be hiding what was stolen, or stealing it, or the one making a fuss to distract people. It was the only time she engaged with me, so there was an element of me that wanted to do it.

I was three or four when Stanley – soon to be my stepfather – appeared. He smelt like an ashtray and had a scratchy beard. Pretty much the first memory I have of him is of sitting on his knee with his finger up my backside. He then went so far beyond that so quickly that while I didn't know what he was doing, I did know it was horrible. That's what I called it – "The Horrible".

In a matter of months I discovered it happened to my sister too. I was angry but powerless. Around the age of five, he started bringing other people around to do The Horrible to me too. I don't know if Jennifer knew. He did it in her space but never in her eyesight. He never said "sex", it was always "in the mood" or "do something" – normal words. When I told my mother, she beat me so brutally that I was out of the picture for a while.

When I was about nine, I told a social worker what Stanley was making me do. She didn't believe me, and when Stanley told her I was forcing myself on him, she wrote that on my files. That note influenced everyone else in authority I tried to tell. Around this time, I was sent to the Wallbridges, a Quaker couple who had tried to help Jennifer in the past. Until then, I'd lived my life as if I was falling through a darkness with no rules. Suddenly everything had a rule. I never told them anything; I loved them. They gave me a way in my head to always find an anchor. Having to leave and go back home was devastating.

In 2000, when I was in my late thirties, my sister told me that Stanley still had access to children. The only way to stop it was to catch him. I arranged with a BBC Newsnight team to confront him, with secret cameras sewn into my clothes. I hadn't seen him for years. There were pictures of kids all over the walls; it was hard to keep calm. He was babbling on, and I couldn't believe I'd thought he was this scary manipulator. He was stupid, just protected by other people's stupidity. Then, in the middle of the conversation, he grabbed me between the legs. I froze. An element of me wanted to attack him, but I knew that would undermine our only chance of protecting some very small children. I knew if I didn't attack, he'd make another move. I got out as quickly as I could, and threw up on the way home.

In 2002, two year after the Newsnight documentary aired, I went to court. Stanley had already been convicted for his assaults on me when I was younger: he'd got three years' probation and was still allowed to live with children. This time, they charged him with offences against myself and my sister and others over a period of 35 years. It was like having a tumour cut from my body while awake – agony, but you know that after, there's a life you can lead. There were 19 charges for Stanley and he was jailed for 15 years. As they read out the verdict, the jury had an unfamiliar look on their faces, and I suddenly realised what it was – for the first time, I recognised what it looked like to be believed.

Shy Keenan is the founder of Phoenix Survivors ( Her autobiography, 'Broken', (Hodder & Stoughton, £12.99) is out now