In a north London suburb last week, a schoolgirl was beaten, gang-raped and then had drain-cleaning fluid poured on her body apparently to destroy DNA evidence. In the eternal cesspit of senseless urban crime, I feel that a dreadful nadir of sorts has been reached, a benchmark of slaked lust and casual, sadistic cruelty. Police sources say the 16-year-old will never fully recover from the injuries caused by the caustic soda and, at the time of writing, she remains under heavy sedation in a burns unit, fighting for her life.
One could weep an ocean for this young woman, her life ruined by these savages, who hunted in a pack like animals and dragged her to an empty house, caring nothing for her wellbeing or future.
Drain cleaner? The callous premeditation is shocking, and underlines the fact that some of the rootless delinquents who roam the London streets are now scraping the bottom of the barrel of humanity.
I'm almost embarrassed to say that the attackers have been described as "five black youths", in case you think I'm being racist in highlighting this crime.
Yes, these are the peculiar times we live in, particularly in a week when Trevor Phillips, the chairman of the Equality and Human Rights Commission, has pointed out that "white flight is accelerating" as Britain becomes increasingly polarised along ethnic lines.
Following the controversy started by the Bishop of Rochester, who said that some Muslim enclaves were "no-go areas" for Christians, it all seems to suggest a country that is becoming increasingly fragmented; a patchwork of rigidly delineated little pockets of race and religion, knots of unyielding humanity who just can't rub along with each other.
This is not a Britain many of us would care to recognise, or even want to live in, although it is true that certain sectors of the middle class are fleeing from inner London like pashmina-wrapped lemmings, desperate to escape the creeping spread of urban decay.
Last year, nearly a quarter of a million decent, law-abiding citizens packed their bags and left the capital for good, seeking what they hope will be a better life elsewhere. They moved to outer boroughs, other city suburbs, rural areas, abroad, the back end of beyond, anywhere but here.
While their fairytale, roses-around-the-door belief in the safety of the countryside and the romantic ideal of a thatched cottage for two is touching, it does point to an underlying urban unease.
I would rather take my chances in the city than the country, but one can hardly blame them for wanting to move.
Elsewhere in London this week, a medical student was stabbed to death in a row over an orange in a Brixton fruit shop. A pupil who was expelled for allegedly having a knife took his school to the High Court. And about the time most of us were sitting down to dinner, watching The Bill on television or putting the children to bed, a teenage girl underwent an unimaginable ordeal in an ordinary suburban street.
What is going to happen to those of us left to live here if youths across the city continue to feel quite comfortable and confident in running amok? That's before you even factor in the older, more professional criminal gangs from more than 25 countries, who operate prosperous drug trafficking, people smuggling, prostitution, money laundering and fraud rackets on the capital's streets.
London is a welcoming city, where home-grown and particularly international criminal networks are flourishing nicely. Somewhere in the city, a great termite nest of law-breaking and corruption grows by the day, nourished by immigrants, some of them illegal, from Algeria, Nigeria, Jamaica and Pakistan, among others.
Is it racist to point that out, too? I don't know any more. All I know is that London has room to absorb them all, particularly as so many of its citizens have recently left in a hurry. And while cosy family evenings by the fire remain one of the few benefits of a wet British winter, how alarming that fewer and fewer people feel safe doing this inside their own homes.