Every day Glenys and her husband, Kevin, hope to hear from their 14-year-old son, Andrew, who disappeared seven months ago in circumstances as mysterious as those surrounding the vanished toddler Madeleine McCann. So far there have been a few leads, but no word from Andrew.
The evening before he vanished was unremarkable. After supper with his parents and sister, Charlotte, 18, Andrew spent an hour making a computer jigsaw with his father.
He then watched some comedy programmes - Mock the Week and That Mitchell and Webb Look - with his mother. "He didn't seem strange, but he was always a quiet, thoughtful boy," says Glenys, 43.
"On Friday September 14, he left for school at 8.05am; we went off to work shortly after. At teatime, he wasn't in his room, but I assumed he was in the basement playing on his Xbox.
When I found his school uniform on the back of a chair in his bedroom, I knew he'd come home and changed. We rang his friends, who said he wasn't with them. They said he hadn't been at school. "
That weekend the police searched the bushes near the Gosdens' home in Doncaster, but found nothing. By Monday, they knew he had taken £250 out of his bank account and had bought a single ticket to King's Cross. Another passenger had seen him on the train, but no one had any idea where the small, bespectacled teenager had gone, or why.
The story of Andrew's disappearance so intrigued Rachel Ford, a television producer, that she is using it to launch Missing Live, a month-long BBC series that highlights individual cases and explores general issues related to the estimated 210,000 people who go missing each year in Britain.
Running away is not a crime, so the hunt for missing people has until now been a low priority for the police and Home Office.
But that is changing. A new police-run national database, which has been operating for a few months, will provide hard facts about the ages, genders and movements of the missing. There are two groups who are most prone to vanishing - young men and older women.
Two thirds of runaways are under 18 and the vast majority return within 48 hours. However, the charity Missing People has 6,000 cases on its books.
Depression, illness, marital problems, debt and mental illness - particularly dementia - are the main reasons why adults leave. Some plot an escape - like John Darwin, who faked death in his canoe to start a new life in Panama; others leave believing their families would be better off without them.
They are usually wrong. Even suicide seems easier for relatives to handle than the limbo of not knowing whether someone is dead or alive, living it up on the other side of the world or lying dazed in the gutter. The burden of anger, uncertainty and guilt is hugely destructive.
Children who go missing have often fought with their families, or are plagued by anxieties. But Glenys Gosden cannot fathom why Andrew decided to leave for London.
"Our only thought is the Reggie Perrin theory - that, like one of his favourite comic characters, he just wanted to step out of conventional life. He'd just seen his sister get A-stars in her GCSEs and, even though he's just as bright - he's very gifted mathematically - maybe he wanted to step off the treadmill."
It's tempting to assume that runaways come from dysfunctional families, but the Gosdens don't fit that picture. Kevin and Glenys are both speech therapists - a profession that makes them "shrewd observers", according to Glenys.
There are Christian texts on the sitting-room shelves, but they haven't baptised their children because "you can't impose your views". Andrew had been reading Nietzsche's Beyond Good and Evil, so she wonders if he liked the idea of being "the superman", "in charge of his own destiny, without guilt or remorse".
Upstairs, his room is full of the books more usually enjoyed by a boy his age - Harry Potter, Alex Ryder, the Roman Mysteries; there's also a snooker table and Marilyn Manson posters. Charlotte's room next door is plastered with Goth material.
"She's dyed her hair black," her mother says, comfortable with teenage experimentation. Her tone changes as she says, almost to herself: "If there was something Andrew didn't feel he could say to us, he didn't give us the chance."
Could he have gone to meet an internet contact? "We've only had a laptop in the house since June and he didn't even want an email address. We've checked the school computers too." Drugs, drink? "He didn't even smoke."
A belief in remaining strong has kept Glenys going through seven months of fear - where is Andrew living; what is he doing for money? - but Kevin collapsed under the strain. "Missing Andrew, going up and down to London searching - I had a nervous breakdown," he says. Charlotte, too, has had a "very tough" time without her brother.
Part of Glenys's self-control is exercised in not blaming anyone for the failure of the investigation. Certainly, there have been blunders and delays that point to how the system could be improved.
For starters, when Andrew didn't turn up at school, the wrong family was contacted. That makes Bob Geldof's proposal, to be broadcast on Missing Live, of a text alert for parents seem a good idea.
But Glenys says it would have made no difference in Andrew's case. "The police wouldn't have done anything that day; they would have assumed he was just playing truant."
The first hours of a search are crucial. One of the police officers in the Gosden case made the kindly, but unwarranted, assumption that Andrew would "just turn up". It was unfortunate, too, that the police didn't trust Glenys and Kevin's conviction that Andrew would head for London because he'd always enjoyed family visits to relatives and museums.
Most serious of all, once he was known to have gone to King's Cross, 24 further days elapsed before his image was found on CCTV footage. Since it was the 27th day since his disappearance, and tapes are routinely wiped after 28 days, it was too late to follow his trail in a city of seven million people.
Further complications arose from the multiplicity of police forces involved - not just South Yorkshire and the Met, but also the parks and the river police.
"We need more co-ordination," says Paul Tuohy, chief executive of Missing People. "A child-rescue alert system exists to send news flashes to radio and television stations, but the police have only used it three or four times in as many years; in the US, they use their 'Amber Alert' system much more often." Madeleine McCann's parents went to the European Parliament in Brussels earlier this month to ask MEPs to set up a further amber alert to track child-abduction cases across borders.
Technological developments could speed up future searches. Number-plate recognition and mobile-phone tracking are proving useful; automatic image tracking - sifting CCTV footage for a distinctive logo or bag - could save countless hours.
Equipment also exists to scan film for unusual incidents, such as a child being separated from a group. Biometric pictures can identify people who are confused or disguised, while age-progression techniques generate images of someone five, 10 or even 20 years on. Already the Gosdens worry that Andrew might look different.
All these developments could release families from the limbo of not knowing. For the moment, though, the Gosdens wait. The police say that because there is no body, they are assuming Andrew is alive, but his parents live on a knife-edge of hope and despair.
Was it their son who was spotted in Brighton recently? Could he have been the boy seen at the Natural History Museum?
Having caused so much pain, he might be frightened of making contact. "I was angry for a time," says Kevin. "I wanted to ask him, 'What is so wrong with a middle-class, middle-income, emotionally supportive family that made you disappear out of the door?'
But now I just want to hug him. Our door is always open, the answerphone is always on. Just tell us you are alive."
• 'Missing Live' is on air from April 21 to May16, BBC1, every weekday from 9.15am to 10am.
• Missing People helplines: sightings 0500 700700, runaways 0808 800 7070.