'It is never too late to do the right thing," implores the viral video message for Madeleine, released this week across the internet. It has been broadcast under the old detective's adage that "everyone has a best friend" -- that someone out there knows what happened to Maddy and, if she is still alive, where she is being kept.
It is the first words of that statement, though, which sum up the essence of how the McCann family are feeling: it is never too late for their child to be returned. Too much time will never have elapsed for them to keep the smouldering flame of hope alive that their little girl will be found.
The message has been released in seven languages and will be promoted around the world by Interpol, police forces and missing persons agencies. It is a huge undertaking, and illustrates clearly that, for Madeleine's parents, the quest to find her is still alive and vital.
The bond between parent and child is one of the most powerful and primal in all human relationships. Maternal bonding begins at the moment of birth -- nature has designed babies to want to breast-feed immediately, and that human contact serves to kick-start an emotional welding that remains throughout the life cycle.
In fact, the relationships children have with their parents -- and some psychological approaches place the greatest emphases on the bond between mother and child -- form the basis for all relationships which follow. Children learn to trust, to value themselves, and to communicate effectively and assertively by interacting with their parents. Theorists such as Freud and Jung suggest that we spend the rest of our lives trying to rediscover the warmth and comfort we found at our mother's breast.
And fathers have an important role, too. It is believed that babies can recognise the timbre of their father's voice while in utero. It is now accepted that while women have a powerful maternal instinct -- a natural drive to reproduce and then nurture their offspring -- men also are gifted with a paternal instinct, a similar desire to further their genetic line and care for and protect their progeny.
Both male and female children will imprint on the father as a very different, though equally important, kind of care-giver to their mother. It is suggested that, even in same-sex couples, one partner will adopt a mothering role, and one a fathering.
The love children feel for their parents, and the love parents feel for their children, is vital and essential. So when that relationship is severed, it brings about the most devastating kind of loss. Yet when that loss is accompanied by the added trauma of an abduction, and not knowing if your child is dead or alive, being cared for or mistreated, the anxiety must be almost unbearable.
But the love of a parent, and the capacity of the human spirit to rise above even the most dire of circumstances and find hope, is truly remarkable. Rational thinking suggests that, after all this time, Madeleine must be dead. She was three years old when she went missing on a family holiday in Portugal in May 2007. The possibilities for what became of her are as numerous as they are wholly unpleasant.
Yet there are instances of children being abducted, held for lengthy periods of time, and then either escaping or being found. The most obvious and recent instance, and one that must have given the McCanns a real boost, is that of Jaycee Lee Dugard, who was abducted aged 11 in Lake Tahoe, California in 1991 and found this year aged 29. She had been kept as a sex slave by her captor, and had several children by him. But, despite the psychological damage of such an ordeal -- and reports suggest that Ms Dugard has many years of therapy ahead of her -- she is alive, and reunited with her parents.
Another case which must have fed the McCanns indomitable will is that of Natascha Kampusch, who was abducted aged 10, in 1998 in Vienna. She was found, aged 18, in 2006.
And that is the dream that the McCanns are clinging to. Regardless of what has happened since that fateful day more than two years ago, they know that, if they could have their daughter back, their love would be enough to heal any wounds.
Though these wounds can be grave, indeed.
Jeremiah Treanor was abducted with his identical twin brother Marcus at age seven in 1980 in London. He was held -- and used -- by a child prostitution ring linked to the Russian Mafia, a group that had carried out 38 kidnappings, of which only 12 children were ever found alive. Jeremiah was one of those lucky enough to be rescued in 1983. Tragically, his brother was murdered by the gang just a week before Scotland Yard shut their operations down.
The man who abducted them -- a father who had lost his own two sons in a car accident -- had told them he was their uncle, and cared for them as his own.
The boys visited him regularly in prison after being reunited with their parents.
The human heart is a complex thing, and parental bonding is powerful beyond our understanding. One can only hope and pray that the McCanns will find their lost little girl, and that, when they do, whoever has had her treated her with kindness. The hope of this is slim, but slender though it may be, it is hope, nonetheless.