Harry, 27, moved from Bristol last year. Its supplies were too erratic for his voracious appetite for heroin and acid. After the deaths of seven people who had not only heard about almost-pure heroin but apparently taken it too, he may be lucky to be alive.
In the early hours of Thursday, 11 March - two days after Harry was told of the new batch of heroin - Francis McCallion, 31, from the Mayfield housing estate outside Edinburgh, was taken to hospital. He had collapsed, gasping for air, in the King's Cross branch of Burger King - one of the all-night fast-food restaurants in this red-light district.
His sister, Catherine, says he bore no resemblance to the standard picture of the desperate junkie who would do anything to get his daily fix. 'He'd been living in London on and off for 15 years and we knew he had taken drugs occasionally,' she said. 'But he never took them when he was in Scotland. He spent five months with me last year and never even spoke to me about drugs.'
He died in hospital on the Saturday. By then, the bodies were turning up. A cleaner found Raymond Wall, a businessman, in the Riviera Hotel in Argyle Square. He too was not an obvious junkie. Unlike most of the square's residents, who live in rooms paid for by the Department of Social Security, or sleep in doorways, he appeared to be a tourist who had booked into the hotel for a night away from his home in Guildford, Surrey. 'He wasn't a drug addict by any means,' Oliver Wall, his father, said last week. 'It's not as simple as that.'
Peter Crone, 27, from Mottingham, south London, was found dead by staff at the Belgrove Hotel, which is in a side street off the square, on 18 March. James McCreadie, Irene Forsyth, 35, and Finton Mallon, 27 - men and women about whom the investigating officers will say little - collapsed and died in the streets. The last body was found on 19 March when a friend of Peter Cargill went into the room they shared at the Ferndale Hotel, a few doors down from the Riviera, and discovered the 21-year-old Irishman dead in bed.
The seven people who died within a few hundred yards of each other in nine days is the largest concentration of drug-related deaths that detectives, doctors and addicts can remember.
The 'hotels' where many of the dead stayed are bed-and-breakfast places used by the homeless unemployed. Prostitutes, drug dealers and thieves selling stolen goods are outside looking for business. So many dirty and infected needles are left on the nearby estates that postmen have refused to deliver there.
King's Cross is a little world of its own, wholly distinct from the expensive suburbs to the north and the commercial heart of London to the south, home to an underclass with nothing to do but inject and sell themselves; to beg, steal and deal. 'These are people who have taken all kinds of drugs for a long time,' said Det Supt Mike Dixon, who is investigating the deaths. 'We're not talking about normal people who follow a normal course of life.'
Perhaps, but relatives and friends say the dead were not freaks or hopeless cases. The manager of the Ferndale, who did not want to be named, said of Peter Cargill: 'He came from Ireland with a friend and stayed for three weeks. He was a nice bloke, a strong, good-looking fella. He wasn't on drugs. I could tell straight away from the eyes.
'I don't know what happened. It's just the effect this area has on people, I guess. They just sit in their rooms all day doing nothing. If you've done drugs once or twice before you'll do them again because you can get hold of them so easily.'
Harry - not his real name - lives at the Ferndale. His knowledge of drugs is encyclopaedic. He has everything he needs in his bedroom drawer: needles and the heroin substitute methadone, which the treatment centre gives him in an attempt to wean him off drugs, and distilled water, blackened spoons and lemon juice for the times when he succumbs to temptation and goes back to heroin.
He and senior police officers are agreed on the most likely cause of the deaths: 'You build up a tolerance if you're used to heroin. You need the strong stuff to feel the buzz. The dealers know a lot of people prefer it strong and I know someone was selling it.'
Dr Howard Baderman, clinical director of the accident and emergency department of the nearby University College Hospital, said the consequences of taking heroin which had not been 'cut' with chalk or baking powder to about 35 per cent strength were often fatal.
'If you are not used to heroin or even if you are an experienced addict who is used to low doses, a high dose will stop you breathing very quickly,' he said.
An ironic twist to the King's Cross deaths is that they came at a time when the police were having unprecedented success against the drug dealers there. Three years ago, crime in the area was getting out of control. Dealers arrived in force, set up their pitches in the station forecourt and sold drugs in broad daylight - 'They were really taking the mickey,' one officer said.
The dealers knew that, under the Police and Criminal Evidence Act, officers were not allowed to force them to open their mouths, so they wrapped 60-milligram balls of heroin (on sale for about pounds 10) and 90-milligram balls of crack cocaine (about pounds 25) in clingfilm and held them in their cheeks.
Det Supt John Farley said that when the police decided to move in they had to rely on good intelligence and new technology to secure convictions. He would not go into details, but it is clear that the King's Cross area is full of police video cameras which provide incontestable evidence.
Video recordings at the Islington police station, where the operation is based, provide a bizarre chronicle of the detectives' work. A fat young man in lurid sports clothes grapples for several minutes to pull his drugs out of his rectum, washes the packages then tucks them into his mouth. A passing woman is clumsily kissed. It looks like a passionate greeting, but in reality he is passing on a ball of drugs.
On the wall of the station the detectives have a list of target dealers. There are Italian names, men who have come from Naples and Sardinia and find, thanks to the Single European Market, that they can claim benefit in London. The Italians deal in heroin, Supt Farley said, the British and Jamaicans in crack.
Commander John Townsend, who is responsible for operations in part of the area, said it was too optimistic to suggest that drug dealing could be eradicated, but there was a real chance that it could be so disrupted that King's Cross would lose its reputation as London's leading dealing centre.
Addicts testify to the operation's success. One said: 'In the old days you could pick and chose, but there've been times recently when if a dealer appeared he would be surrounded by people who were so strung out they were manic.' But the cameras can only collect evidence during the day; the night belongs to the dealers. On Thursday night I saw deals every few minutes. A woman in a red skirt sauntered up to a group of girls. Two men bumped into each other. The parties stoop, you catch a glimpse of the notes, and it is all over.
Harry, who emphasised that he does not deal, said he thought drugs would always be in King's Cross. 'You can still buy a bag of heroin for pounds 50. You get one shot yourself, cut the rest up into 10 portions and sell them for pounds 10 each. That's a hundred per cent profit . . . That's a good deal for people round here.'