On 25 January 2006, officials from a north London housing association repossessing a bedsit in Wood Green owing to rent arrears made a grim discovery. Lying on the sofa was the skeleton of a 38-year-old woman who had been dead for almost three years. In a corner of the room the television set was still on, tuned to BBC1, and a small pile of unopened Christmas presents lay on the floor. Washing up was heaped in the kitchen sink and a mountain of post lay behind the front door. Food in the refrigerator was marked with 2003 expiry dates. The dead woman's body was so badly decomposed it could only be identified by comparing dental records with an old holiday photograph of her smiling. Her name was revealed to be Joyce Carol Vincent.

I first heard about Joyce when I picked up a discarded copy of the Sun on a London underground train. The paper reported the gothic circumstances of her death – "Woman dead in flat for three years: skeleton of Joyce found on sofa with telly still on" – but revealed almost nothing about her life. There was not even a photograph of her.

The image of the television flickering over her decomposing body haunted me as I got off the train on to the crowded platform. In a city such as London, home to 8 million people, how could someone's absence go unnoticed for so long? Who was Joyce Vincent? What was she like? How could she have been forgotten?

News of Joyce's death quickly made it into the global media, which registered shock at the lack of community spirit in the UK. The story ran on in the British press, but still no photograph of Joyce appeared and little personal information.

Soon Joyce dropped out of the news. I watched as people discussed her in internet chatrooms, wondering if she was an urban myth, or talking about her as though she never mattered, calling her a couch potato, and posting comments such as: "What's really sad is no one noticed she was missing – must have been one miserable bitch." And then even that kind of commentary vanished.

But I couldn't let go. I didn't want her to be forgotten. I decided I must make a film about her.

At this point all that had been revealed in the press was that Joyce Vincent was 38 when she died, had been born in west London to parents who were from the Caribbean, and that some of her family had attended her inquest. Some reports suggested Joyce was, or had been, engaged to be married, and that before living in the bedsit she had been in a refuge for victims of domestic violence. But she didn't fit the typical profile of someone who might die and be forgotten: she wasn't old without family; she wasn't a loner, or an overdosed drug addict; nor was she an isolated heavy drinker. Who she was and the circumstances of her death were a mystery.

I placed adverts with various publications and internet sites. On a poster on the side of a black cab I asked: Did you know Joyce Vincent? Meanwhile, as I waited for any response, I contacted people who were involved with bringing Joyce's story to light.

I met Alison Campsie, news editor for the Tottenham & Wood Green Journal, whose journalist David Gibbs had reported on Joyce Vincent's inquest. She told me that while the paper would have liked to have pursued the background to the story, they didn't have the time or money, and that even the BBC with all its resources had tried and failed to run an item on Joyce.

In the Three Compasses pub below her office, I talked to Lynne Featherstone, MP for Hornsey and Wood Green, Joyce's constituency. Lynne had urged the police to reopen their investigation into Joyce's death but they decided there was nothing to answer to in terms of foul play. The coroner recorded an open verdict, with the cause of Joyce's death "unascertained". "We don't know how big a part Joyce played in her own isolation or whether it was more down to society neglecting her," Lynne told me.

Lynne wrote to the local council, the utility companies, and the housing association about Joyce's unpaid bills, questioning why alarm bells didn't ring earlier – but she either received no reply or little insight. "The point is, Joyce Vincent is dead, no one murdered her, and no one seems to care that much. I gather she was very beautiful, which for reasons totally spurious makes it more poignant because we always think beautiful people have everything go their way."

On the way to her next appointment Lynne drove me to Wood Green, to the back of Shopping City, where lorries rumbled in and out of a delivery depot. She pointed to the housing estate above the mall known locally as Sky City, where Joyce had lived and died. I looked at the red brick walkways and tiers of water-stained grey concrete, interspersed with metal grilles, indistinguishable from the car park or the shopping centre below. "I suppose, in a way, we all walked by," Lynne said. As I stepped out of her car she wished me luck.

Dominating the skyline was a round blue sign for Shopping City – a beacon to commercialism. In one of the flats I saw an open window with a billowing net curtain and I thought of the window in Joyce's bedsit that had been open for the two years she lay dead, insects crawling along the windowsill, the escaping smell of her decomposing body attributed to the rubbish bins below. I walked around to the other side of the complex – to the high street, hectic with shopping activity and traffic. The main door Joyce used to access her part of the estate is here, sandwiched between the usual chain of shops.

Inside the entrance I avoided the lift and climbed the empty grey concrete stairs. I walked along a walkway, meeting nobody. In contrast to the hordes of people below, it was desolate. I found Joyce's bedsit, with its glossy green door, at the end of the walkway. With only one neighbouring flat, and no flat above or below, it felt architecturally cut off. I knocked on the doors of other flats in the block, but no one answered. I wondered if I would ever meet anyone who actually knew Joyce.

The first response to my adverts was from Karen, but it turned out she never knew Joyce. "I was a neighbour. I lived on her doorstep. I got my old diaries out. Had I seen her? Had I written about her? All the neighbours – where were we? Why didn't we talk to her?" Karen said she had always liked living in Sky City but that as she lives alone, and is the same age as Joyce was when she died, she now worries whether anyone would notice if anything happened to her.

Months passed. I spent time in libraries and public records offices, piecing together some of Joyce's history through official records, locating previous addresses and relatives. I managed to track down people who knew Joyce, but they wouldn't talk to me. Then I received an email from Martin Lister, who had seen my advertisement. He wrote to me in the hope that the Joyce in question was not the same Joyce he went out with in his twenties. We quickly established that it was. On the phone he said it just didn't add up – "she never drank much, she never took drugs" – but the thing that most surprised him, he said, was that she ended up in social housing.

I arranged to meet Martin outside Shepherd's Bush underground station. In his late 40s, he wore a green Brazil baseball cap, and was all friendly smiles. In his local pub I thanked him for seeing me. "Well I want to thank you," he said, his pale complexion flushing pink. "Therapy, is how I feel about it."

While he had confided the news of the circumstances of Joyce's death to friends, he was glad to have the opportunity to discuss her at length. They had met in 1985, when he worked negotiating client renewals for a shipping company in the City. Joyce was 20 years old and secretary to his boss. "She was always asking me to go for a drink, but it never occurred to me that she was asking me out. I thought, what a shame she doesn't have any friends. I didn't read anything into it."

Eventually Martin went for a drink with Joyce and they subsequently dated for about three years. Afterwards they kept in touch, on and off, until 2002. Looking back, Martin was unsure if he ever knew exactly what was going on in Joyce's life. "You look back and think, I wish I'd asked more, wish I'd understood more."

They had good times together. "We were always doing something," Martin reminisced, "racing at Goodwood, tennis at Wimbledon, classical music, opera. We liked restaurants too." Martin shook his head, baffled at Joyce's outcome. "She always wanted to improve her mind. Actually, she told me she'd had elocution lessons and she sounded – I wouldn't say posh, but you wouldn't know she was from London, she just sounded very well-spoken, almost BBC really. In reality she grew up off the Fulham Palace Road in west London and she used to say, 'I don't know why people say it's so lovely round there because it certainly wasn't when I was growing up.'"

Pulling some photographs from a carrier bag, Martin looked at one wistfully before handing it to me. It was the first photograph of Joyce I had seen. I held it carefully, trying to take in every detail. "People used to say she looked like Whitney Houston," Martin said proudly. He sipped his wine and looked at another photo. "Her hair came from her mother's side. Her mother was Indian, she died when Joyce was young, 11, I think. She had a real bond with her mum, especially as she was the youngest. She had four sisters, but I think she was the only one to be born over here – the sisters brought her up really. Her dad was a carpenter. I never met her family, which I thought was a bit odd.

"I don't understand. She worked her way up, had really good jobs. She earned excellent money." His voice was tinged with sadness as he said: "Apparently she wanted to marry me, but being a typical bloke I was like – no, no, don't be ridiculous. I didn't want to settle down."

Martin opened a sizeable old Filofax to find Joyce's name. Her contact details had been TippExed over a number of times. "It was alarming really, how often she moved – at least once a year."

I asked Martin to appear in my film. I stressed how Joyce's story was a very modern one. She was born in 1965, the year the Post Office Tower opened, which Tony Benn later referred to as a symbol of our age – an age in which we worship the internet, television, mobile phones. I told him how ironic I thought it that Joyce should be forgotten and unreachable in this so-called period of communication.

Martin listened politely, thought for a while, and then said, "We'll see". It was not until a few years later, sitting in the same pub, that he finally agreed. "I can't say no, I've got to do it for her," he said then.

A few weeks after meeting Martin, I went to the Horn Pub in St Albans with John Ioannou, who was once friendly with both Martin and Joyce. Known as John the Greek, he was exuberant and talkative. He recalled reading the story about Joyce in a newspaper, but didn't connect it to the Joyce with whom he had once shared a house for a while. He told me he felt an enormous amount of guilt because he spoke to her on the phone in 2002, but never found the time to meet her.

He described his gang of home-counties friends whom Joyce had hung out with in the 80s. "We were a bunch of blaggers. We did things way above our class. A few of us came from money, but most of us didn't. We used to mix with proper posh people and go sailing, go to glitzy nightclubs. Right poseurs we were. We used to make up names. Joyce called herself Rachel Prejudice."

I showed him the photographs I'd gathered of Joyce. "The trouble with Joyce was she was very fanciable," he said. "Wherever she went and whatever she did, there were people trying to get her into bed. It was a burden that she was so beautiful and she was very clever, a lot more intelligent than she let on. I think she had several lives."

John asked what had attracted me to Joyce. I replied that I couldn't leave her to be forgotten – and that I had discovered there were a lot of things that connected us: we were exactly the same age, we shared a name – Carol, her middle name – and at one point we even lived on the same street. Joyce lost her mother when she was 11 and I was 11 when my father died, so I felt I understood something of the loss she had suffered. I told John that the title of the film,Dreams of a Life, captured what I was trying to do – dream up Joyce's life and ambitions through the information I gathered and the people who knew her.

John said: "I want to know Joyce's story myself, and that sounds ridiculous coming from someone who knew her. There must have been signs she would end this way, but if there were she covered them up with this happy-go-lucky, having-a-great-time act." John shook his head and sighed. "She died of neglect. We all loved her, but not enough to stop her dying."

On the train back to London, I reflected on how nobody she knew really worried about Joyce when she fell out of touch with them, as she often did – they just thought she was off somewhere having a better life than they were. Her aspirations and desires, her immaculate way of presenting herself, masked any deeper troubles she may have had.

As I continued my research I tracked down some of Joyce's former colleagues who were willing to appear in the film. Kim Bacon and Dan Roberts worked with Joyce at Ernst & Young, one of the biggest accountancy firms in the world. They told me Joyce worked for the company for four years and had a very responsible job in the treasury department, "moving the company's money around". It was during this period that Joyce was engaged for two years to someone I tracked down but who wishes to remain anonymous.

Her colleagues were surprised when she decided to quit in 2001. Kim said: "There do seem to be conflicting stories about what she did when she left." Joyce told some people she was going travelling with 20 people, and others that she had been headhunted. All that is known for sure about what happened to her in the time between her departure from the firm and her death is that she spent some time in a refuge for victims of domestic violence in Haringey.

Dan said: "I know it sounds odd, but it seems like we're talking about two different people. I just can't connect the Joyce who died to the Joyce that we knew." Kim nodded in agreement: "I mean she gave this impression of being a happy, bubbly person but it does make you wonder what was really going on."

I showed them the Sun article that started my quest. Kim studied the accompanying photograph of the bedsit. "The place she ended up living in doesn't tie up with her persona. I always imagined she lived in a really nice Victorian house, lovely furniture, nice things around her, everything immaculate and perfect. Not somewhere like that."

They looked at the photos of Joyce I'd gathered. "This is the sort of thing you'd imagine being on Facebook," Kim said. Dan agreed – "but we didn't have Facebook then. It's different now, you can keep in touch with people very easily." Dan looked around the pub we were in, where they used to socialise with Joyce. "It's shocking to think that two years after she left work she was dead," he said. Kim put the photos down. "I really don't understand," she said. "She was a very popular girl and I don't know why we didn't keep in touch. I feel a bit guilty about that."

As time went on I received a lot of messages via Friends Reunited from Joyce's old schoolfriends. All concurred that she was beautiful, well turned out, funny, down to earth, and all mentioned that she loved to sing – one message even urged me to tell the world about Joyce's fantastic singing voice.

It was two more years before I found Kirk Thorne, a musician, and a friend and landlord of Joyce's in the late 80s. Kirk had once recorded Joyce in his studio.

I sat with him in the garden of the same modern house in Wapping that Joyce had once occupied. He told me that since he received my message about Joyce he had spent hours speculating on how she ended up as she did. "I can't understand. She had a lot of friends and a good social life. She was not a girl that came in and sat in front of the telly. If she was white she could have been a debutante – she was upwardly mobile, a high flyer."

Kirk was especially surprised that by the age of 38, Joyce was living without a man. "Joyce was the kind of person that would worry most women. She was a threat. Good-looking, intelligent, successful and on a mission for the type of man all women are after."

He showed me around the studio he had built at the bottom of his garden. It was here that Joyce once dressed up as a maid and served tea to Captain Sensible, the punk legend. It was also here that she first fulfilled her dream of being a recording artist. Kirk had lost the tape, though at my insistence he promised me he would have another hunt for it. He wondered if Joyce might have been happier if she had pursued her singing and taken a different path in life. "She had a clique with all these City bankers – they didn't suit her, but she liked it," Kirk said. "I think she was on a search for something she wasn't going to find. I used to think that what she needed was a good black man. She was my flatmate, not my family, so I didn't tell her."

Catherine Clarke became good friends with Joyce while renting a room in Kirk's house. I tracked her down in Florida, where she recalled that Joyce only had one other close female friend. "Mostly it was men. Men who had crushes on her, men who followed her – there was always a story about a guy that had the hots for her. It was just unbelievable how intense guys would get with her."

Catherine said she was not surprised that Joyce ended up in a refuge for victims of domestic violence. "Guys would come on so heavy and not let go. I can only think she became isolated from her family because of a guy that she chose. Maybe she was ashamed of the situation she got herself into. To go into a women's refuge, for Joyce, would have been a big thing."

I tracked down another of Joyce's friend's – the American disco singer Judy Cheeks, who once took Joyce out to dinner with Stevie Wonder. On the phone from the States, Judy said she last spoke to Joyce in the late 90s and found her still looking for Mr Right. "I had no idea where she was heading. It appears no one did. I often thought of her and always assumed she had finally found her ideal husband, had a few kids and was happy."

Over time I received a number of phone calls from Joyce's former boyfriends. Mostly they were calling me for information, so disturbed were they that the Joyce they went out with could have ended up being so overlooked. Most of them didn't want to appear in the film, but were willing to give me snippets of information. Jason, for example, told me that when he met Joyce he was a working-class boy from a sink estate, and Joyce was five years older than him and wanted to be a pop star. "I used to resent her for that. I used to resent her for having dreams… what a fall from grace." Jason told me that before he went out with her, Joyce went out with a baronet and an MP, but he couldn't recall their names. He also thought that Joyce once knew the American soul singer Betty Wright.

So I wrote to Betty in Miami. A couple of months later I received a phone call from Alistair Abrahams, Betty's one-time tour manager and Joyce's former boyfriend. Betty had told him about my letter. Stunned by the news, he invited me over to see him in London the following day.

In his early 50s, with long dreadlocks swept back behind his shoulders, Alistair showed me into his living room. Originally from Zimbabwe, he delivered his accented words slowly and cautiously as he described Joyce and the two years they lived together in the early 90s. "There were a lot of exciting things happening to me and her arrival coincided with a lot of that change, so I used to call her my lucky charm. She was always immaculately attired down to the bows on her underwear. But she wasn't just physically beautiful, she had an aura about her."

Alistair explained that Joyce never really talked about her life before she met him. "Have you ever seen the movie The Man with No Name? That's how she was – she came with no past."

While Joyce lived with Alistair she came into contact with many of the musicians he knew and worked with. "We had great times. We had Jimmy Cliff to stay at the house, Gil Scott-Heron and Isaac Hayes came for dinner. For her it was exciting, vibrant, thrilling. It was a good time."

He asked me if I had found out how Joyce had died but I told him that not even the pathologist came to a conclusion. "Perhaps she suffered a fatal asthma attack, or do you think it was something more sinister?" he asked. I replied that Joyce's death would always be shrouded in mystery and open to speculation, but what was more important then dwelling on how she died was to remember her life.

"I was so committed to Joyce almost in a paternal way. I think that's what she wanted out of a relationship, someone she could rely and depend on. She was a chameleon in many ways – she adapted to the environment she was in. I introduced her to Ben E King and the next day she bought his album. After I'd introduced her to Gil Scott-Heron, when she met him again, she had this wonderful knowledge of him, she was asking him questions about the civil-rights movement and The Revolution Will Not Be Televised."

Alistair recalled the time he surprised Joyce by taking her to Wembley in 1990 to see a Nelson Mandela tribute concert. "Something very momentous happened – she met Nelson Mandela, she shook his hand. In fact I spoke to my brother yesterday and he thinks he may have seen her at the concert, when it was on the TV."

I ordered up the film of the concert, Nelson Mandela, International Tribute for a Free South Africa, from the BFI National Archive. I trawled through it, ever hopeful, constantly pausing when I spotted anyone remotely resembling Joyce. After a few fruitless hours I began to prepare myself for disappointment when the programme cut from the stadium crowds to Nelson Mandela backstage, addressing the musicians who had taken part in the show. As he ended his passionate speech they cheered in appreciation, and there was a cut to a wide shot from the rear of the room – featuring an array of backs of heads.

And then I saw her. It was Joyce, unarguably. She turned and smiled at someone behind her. Catching the light, her earrings gleamed. She turned back and I panicked, I had lost her.

But she turned around once more. It was Joyce – moving and alive. I had found her. The power of the moving image hit me, the power to resurrect.

I rewound the tape and timed Joyce's appearance. Four seconds. I slowed the footage down and watched. One hundred frames, hundreds of dancing pixels.

Joyce, who died alone in her bedsit, anonymous and seemingly forgotten, had once had her image transmitted live to millions of living rooms in the 61 countries where the show was broadcast.

The video cut away from Joyce to the Wembley crowd and I thought of her, backstage, in her element, on a high, talking to Anita Baker and Denzel Washington, shaking hands with Nelson Mandela, in a room with verifiable stars. She was 26 years old, ambitious, beautiful, full of hope for the future. She had her whole life ahead of her but in 13 years she would die and nobody would know and nobody would notice.

I resumed the tape and carried on watching the show, eager to experience what Joyce once had. Nelson Mandela arrived on stage to rapturous applause and the crowd sang, louder and louder, "You'll never walk alone".

Dreams of a Life, written and directed by Carol Morley, will be shown at the 2011BFI London Film Festival. The film has been shortlisted for the Grierson award for best documentary at the LFF. It will go on general release in March 2012.www.dreamsofalife.com

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