Thieving, begging, mugging, stealing were the only ways the addict could feed the need.

On a housing estate in south-east London, the trail marked out for one little share of Afghanistan's poppy harvest came to an end.

Malachy knew her life story, and more. He had been led into each cranny of her existence. He sat opposite Mrs Mildred Johnson and drank tea poured through a strainer that caught most of the leaves, a present from a distant relative on her wedding day. He ate ham and cucumber sandwiches, her late husband's favourite filling for his lunch when he'd driven a double-decker bus in London.

Not expected to talk, only to listen, he occasionally nodded and tried to be attentive. He knew her life story because the same mixture of anecdote and memory was served up each fortnight, but he never showed signs of boredom or irritation at the repetition. He would be there for two hours. She had a small carriage clock with a tinkling chime – a present from her nephew, Tony – and at four o'clock on the first and third Thursday in the month the knock would come on the wall, and at six o'clock, without ceremony, and always the refusal that he should wash up the cups, saucers and plates, when the hour was struck, he would be told that it was time for her to dress to go out to bingo. He was then dismissed.

He knew she was seventy-four. She had been widowed twelve years back after thirty-nine years of marriage. Her husband, Phil, had left no money and she survived on the state's meagre generosity. Her elder brother, Graham, and her sister-in-law, Hettie, were dead. Her only living relative was her nephew, Graham and Hettie's son, Tony – something important in the police', and she'd snort.

He thought she must spend the first three hours of each day scrubbing, cleaning, dusting her one-bedroomed flat. It was spotless. If a crumb from a sandwich fell from his mouth, Malachy was always careful, immediately, to pick it off his trousers so that it should not fall to the carpet.