Tommy Brennan died on a Tuesday, which was inconvenient for everyone. He had run the Wheatsheaf Arms on Vallance Road for thirty-one years, and in that time the pub had become something more than a pub. It was a routing station. A clearing house. A junction box through which flowed favours, rumours, small loans, introductions, warnings, and the thousand invisible transactions that keep a neighbourhood from coming apart. When Tommy's heart stopped behind the bar at ten past four in the afternoon, surrounded by half-pulled pints and the smell of stale Woodbines, the junction box went dead. The network did not die, not immediately, but it began the long slow process of discovering how much of itself had depended on one fat Irishman with a bad cough and a genius for remembering who owed what to whom.

Maggie Chen heard about it from Ravi Patel, who knocked on the door of her flat above the chippy on Bethnal Green Road at half past five. She was working piecework, a dozen rayon blouses for a wholesaler in Brick Lane, and her Singer machine was clattering so loud she almost did not hear the knock. Ravi stood in the doorway holding a copy of the Evening Standard and looking like a man who had just watched his bank burn down.

He is dead, Ravi said. Tommy Brennan. Heart.

Maggie let the foot pedal stop. The silence was enormous. She had been in London twelve years, ever since her parents sent her from Hong Kong at seventeen with two hundred pounds and the address of an uncle who turned out to have moved to Manchester. The Wheatsheaf was the first place she ever felt like she belonged. Tommy had let her use the back room for a clothing exchange, a sort of informal market where the women of the neighbourhood could trade and sell. He never asked for rent, never asked for a cut, only said that if she ever heard of anyone needing a room, or a job, or a doctor who would not ask questions, she should let him know. That was how the Wheatsheaf worked. You paid in connections.

She had been saving to bring her younger sister over. Tommy was supposed to help with the paperwork. He knew someone at the Home Office, or knew someone who knew someone. Now the chain was broken.

Dennis O'Leary was sitting in the Wheatsheaf when Tommy died, and Dennis was the one who watched him go down. One moment Tommy was pulling a pint of Guinness, the next he was on the floor with his face turning the colour of old candle wax. Dennis had been a docker until the London Docks closed in sixty-nine. Then he had been a warehouseman until the warehouse moved to Basildon. Then he had been on the dole for six years, and then he had stopped being anything at all except a regular at the Wheatsheaf, where Tommy let him run a tab that never seemed to come due. Dennis had not paid for a pint in eighteen months. He knew Tommy was carrying him. Everyone knew. But Tommy never mentioned it, never even looked at Dennis with that particular pity that working men learn to recognise and dread. He just poured the Guinness and asked about Dennis's son, who was up in Glasgow working on the rigs.

Now Tommy was dead and Dennis was forty-seven years old, standing outside a pub that would probably be bought by a developer and turned into flats for people who worked in the City. The Docklands were already changing. The cranes were going up. Thatcher's Britain was a place where old fat Irish publicans and unemployed dockers had no function, no place in the wiring diagram. Dennis stood on the pavement and felt himself becoming invisible.

Ravi Patel had a different problem. The corner shop on Cambridge Heath Road was a family business, his father's and now his, and it survived on the thinnest of margins. The secret to survival was the informal credit network that Tommy Brennan had orchestrated through the Wheatsheaf. Ravi would extend credit to a family — perhaps fifty pounds for a month of groceries — and Tommy would vouch for them, would know if they were good for it, would gently remind them if they fell behind. Tommy was the guarantor, the social collateral, the human credit rating agency for three streets in every direction. Without him, Ravi would have to call in debts. People would not be able to pay. The whole fragile system would collapse.

The problem was not the money. Ravi could absorb the losses. The problem was that once you started asking for payment, you stopped being a neighbour and became a creditor. The shop would survive, but the relationship would not.

Eileen Fletcher came down from Leeds on the Wednesday morning train. She was twenty-one and reading sociology at the university there, the first in the family, the one who was supposed to get out. Tommy was her father's cousin, not her father, but he had been more present than her father ever was. When she was fifteen and wanted to know about the Dublin she had never seen, Tommy told her stories about Stoneybatter and the Liffey until her mother shouted at them to stop keeping her up past midnight. When she got her A-level results, Tommy put fifty pounds in an envelope and slid it across the bar without saying a word.

She stood in the empty pub the morning after the funeral, the chairs still up on the tables, the air thick with the ghosts of ten thousand cigarettes, and she thought about the word node. She had learned it in a lecture on social network theory. A node is a point of intersection. A person through whom information and resources flow. Remove the node, and you remove the connections. You do not just lose the person; you lose every pathway they maintained. The network does not always recover. Sometimes it fragments into smaller networks that cannot reach each other. Sometimes it simply dissolves.

Maggie Chen found a solicitor who specialised in immigration. It cost her three hundred pounds she did not have. The solicitor said the application would take at least eighteen months, probably longer, and there were no guarantees. Maggie sat in her flat above the chippy and looked at the half-finished blouses and thought about her sister, who was seventeen now and would be nineteen by the time the paperwork went through, assuming it went through at all. She had lost eighteen months. She had lost her connector. She was not angry, not exactly. Tommy had been good to her. But the system that depended on one man's memory and one man's goodwill was a fragile system, and it had broken.

Dennis O'Leary walked into the Wheatsheaf on the Friday after the funeral and found a sign on the door: CLOSED UNTIL FURTHER NOTICE. The brewery was sending someone to assess the premises. Dennis had heard rumours of a buyout offer, something about redevelopment. He stood on the pavement for a long time, hands in the pockets of a coat that had been new in 1978, and then he walked to the off-licence on the corner and bought four cans of Skol with money he had borrowed from Ravi. He drank them on a bench in Weavers Fields, watching the new flats going up on the skyline. The cranes moved against the grey sky like the necks of prehistoric birds.

Ravi Patel called in his debts. He had no choice. Without Tommy's vouching and Tommy's gentle reminders, the credit chain had no guarantee. Some people paid. Some people did not. Some people stopped coming to the shop altogether, embarrassed or resentful or simply unable to face him. Ravi kept the shop open, but the warmth went out of it. He became a shopkeeper, not a neighbour. The distinction was subtle but absolute.

Eileen Fletcher went back to Leeds and changed her dissertation topic. She wanted to write about informal networks, about the invisible architecture of working-class communities, about what happens when you pull one brick from the arch and the whole structure shifts. Her supervisor said it was interesting but not sociological enough. Perhaps something on youth subcultures instead. Eileen wrote the paper anyway, in her spare time, late at night when her flatmates were asleep. She did not show it to anyone.

Gerry Simms had been using the Wheatsheaf for five years as an organising base. He was a Labour councillor for the ward, one of the old guard, a man who believed that politics happened not in committee rooms but in pubs and church halls and outside factory gates. Tommy let him hold meetings in the back room on Tuesday nights. The residents' association, the tenants' union, the campaign against the poll tax that was still two years from becoming law but was already being whispered about in Whitehall. Without the back room, the meetings moved to a dusty hall above a launderette on Roman Road, and attendance dropped by half. People did not want to sit in a cold hall. They wanted to sit in a warm pub with a pint in their hand and Tommy Brennan behind the bar, nodding along to the arguments and occasionally interjecting with something profane and true.

The poll tax consultation went ahead. The residents had no organised response. The council passed the measure without meaningful opposition. Gerry Simms stood up in the council chamber and made a speech about community and connection and the death of public houses, and his colleagues looked at their watches and thought about lunch.

Six months after Tommy died, the Wheatsheaf Arms was sold to a development company. They gutted the interior, knocked through the back wall, and turned the whole thing into four luxury flats with exposed brickwork and spiral staircases. Young professionals from the City moved in. They paid three hundred thousand pounds each and complained about the noise from the market on Brick Lane.

The network did not die. That would be too clean a story. It fragmented. It rearranged itself into smaller, less efficient clusters. Maggie Chen found a new solicitor through a woman she met at the laundrette, a Pakistani grandmother who knew a barrister in Ilford who handled immigration cases. Her sister arrived in 1987, two years later than planned, and the two of them started a small alterations shop near Columbia Road. Dennis O'Leary stopped drinking in the spring of 1986, not because of any revelation but because he ran out of money and ran out of credit and sat on a bench in Weavers Fields and realised he had been sitting on that bench for thirty-seven consecutive days. He got a job cleaning offices in Canary Wharf, the great glass towers rising from the ruins of the docks where he used to work. The irony was not lost on him. Ravi Patel sold the corner shop to a chain of convenience stores in 1988, took the money, and opened a restaurant in Walthamstow that served the best paneer tikka in north-east London and did not extend credit to anyone. Eileen Fletcher finished her degree, got a job in local government, and spent twenty-five years running community development programmes in some of the poorest wards in the country. She never forgot the word node.

Gerry Simms lost his council seat in 1990, the year the poll tax riots broke out across London. He stood in Trafalgar Square on the thirty-first of March and watched the police horses charge the crowd, and he thought about Tommy Brennan pulling pints in a pub that no longer existed, and he wondered what would have been different if one fat Irishman's heart had held out for another five years.

The Wheatsheaf Arms is luxury flats now. The people who live there do not know what it used to be. They do not know about the connections that ran through that space, the favours and rumours and loans and introductions, the invisible wiring that powered a community for thirty-one years. They do not know Tommy Brennan's name. The network has rebuilt itself, as networks do, finding new nodes and new pathways and new junctions. But it is not the same network, and it never will be, because networks are not interchangeable. They are specific. They are local. They are held together by particular people in particular places, and when those people go, something goes with them that cannot be replaced.