The tunnels of the New York subway are home to a subterranean community of people known as the 'Molemen'. It is Captain Bryan Henry's job to help them see the light
olice Captain Bryan Henry is the kind of man who inspires confidence. Well over six feet tall, black, handsome, and unfailingly articulate, he was good to have along as we descended through the steaming tunnels underneath Manhattan's Grand Central Station, passing hissing, sputtering steam jets, joists and pipes, ducts of every size. Startled by an unexpected clank, I'd turn expecting to face a cowering or towering human with baleful eyes. But all that was there was the occasional discolored sock and shirt jammed into a hiding place, proof that someone, sometime, called this hostile enviroment home.

We were on the prowl for the Molemen: people who live in the vast network of tunnels that extends beneath New York. Depending on whom you believe, anywhere from 1,000 to 5,000 people make their homes in this ill-smelling, dark, damp, noisy hell. One thing is certain: not one of them wants to be found; and a good number of them are armed. If one of them leapt into view, I wanted Captain Henry in earshot.

Captain Henry, however, was not sure we would find anyone at all. In 1989, when he first went on underground reconnaissance, there were some 300 transient and permanent homeless people living in Grand Central Station, and perhaps 60 of them holed up in the tunnels beneath. Now, through vigilance, and through his own efforts to hook up the Molemen with outreach programmes, the numbers are far diminished-at least at Grand Central. "There's a lot of mythology," he told me. "You hear everything - that there are mutants, and Chuds - Cannibalistic Humanoid Underground Dwellers." (There aren't).

The grim underworld of the subway is a dangerous place - hazards include asbestos and tricky electrified railway tracks, not to mention the occasional train that crushes the unwary. Captain Henry had just been explaining why it was that the Molemen used to come down to the tunnels in the bad old days (it's warm, private, and conducive to unharassed crack-smoking) when he hissed, "Shhhh!" and began to walk even faster. Then I heard him call out "Hello, there!" and as I caught up, a shape emerged out of the cramped dark.

"Come here for a second," Captain Henry cajoled. A small young woman, black, covered in an overcoat and baggy trousers, carrying a luxury cosmetic store bag, stood blinking in the light of his torch.

"Do I know you?" Captain Henry asked. "How'd you get here?" The woman smiled agreeably and said nothing at all. "I'm not here to mess with you," he told her. "Down here you can get a lot worse people bothering you than me." She listened, inattentively, still smiling. "I know a woman couple months ago who was living down here. She got knocked up, got raped," he said chidingly. "Being arrested is not the worst thing that can happen to you. How long have you been down here?" The woman finally spoke. "Just a little while," she said. "A couple months."

Her name was Shaniqua. He asked her about her family, her children, then led to the punch: "I can hook you up with an outreach programme if you like," he suggested. "I'll do it, she said, in a faint, wispy, out-of- it voice. He let her go, back up to the station, several levels above.

"The bottom line is, this is a nice warm place to live," said Captain Henry as we walked on. "But she could be beaten up, raped, robbed, bitten by rats, abused. She's probably a chronic crack abuser."

A large cockroach skittered past. Captain Henry showed off new lights that have been installed in the doorways and narrow corridors that line the tracks, to hinder the homeless people from nesting. He pointed out metal cages built around machinery and building materials to keep out squatters. "It's not as comfortable for homeless here as it used to be. We're cleaning things up, we got lights everywhere ... what's this?" Looking with his flashlight behind a low, broken concrete wall, Captain Henry had found another Moleman. This man lay sleeping in the dark, wrapped in blankets. "Keep your hands behind your head," Captain Henry ordered him, more sternly than he talked to Shaniqua. "Put your shoes on."

"I got no weapon," a voice replied. In the light of the torch I saw a Hispanic man in his late forties, smiling in an attempt to appease. "What are you doing living like this," asked Captain Henry indignantly. "I used to work," the man says in a cigarette rasp, fumbling through the clutter of his bed. "I owned a truck a long time ago. It all went bad. I gambled it away."

"There is no reason for anybody with a driver's license to live like this," chided Henry. "You could drive a cab, an ambulance, a limo, a truck, you could be making a living. What if you some nut tried to set fire to these papers? You'd be like roast pig. You get anyone down here with evil in their heart, and you're not going to know what happened to you. Would you like to talk to a social worker? I can hook you up with one. Tell him Captain Henry sent you. You decide."

We left the man with firm instructions to head upwards, and kept walking down the endless miles of track, stumbling over broken tiles and rubble. "You get some mentally ill people threatening you, but mostly these people are harmless," Captain Henry said. "They mostly have knives, razors, boxcutters - but that's for self-defence. I've been attacked by emotionally disturbed people, but then I call in backup. Usually you can tell from a distance what you're dealing with."

Before he was with the Metro-North police, Captain Henry was a paramedic at Bellevue, which gave him experience of every kind of trauma "from literal life and death situations to hangnails." That makes him especially able to judge the Molemen. "When I meet them, I make an assessment of their state of mind and health. Like Shaniqua - I called her the same way you'd call a child, I didn't yell, 'Freeze, police!' That's experience."

Under the mental hygiene laws, Captain Henry is allowed to remove people against their will and recommend them to hospital care, if he judges them to be dangerous to themselves.

He also is entitled to arrest any of the people we have met, for criminal trespassing. Mostly, though, he simply tries to remind them that they are human beings, not Molemen, not Chuds, not rats, and to move them to improve their own lives. "If they respond positively, we've been able to reunite them with their families, and with drug treatment programs, and find them housing entitlements."

His reward, he says, is when one of the homeless men and women he has rescued walks through the door of his office, and he doesn't recognize them, because they've cleaned up. "It's a very emotionally charged moment," he tells me. "When somebody comes back and they've reunited with their family, or gone into a program, if they stick to it, that's my payback."

And then he finds Brenda, who is far from payback time. She is a woman Captain Henry found and helped in 1993, leading her out of the tunnels and to the hospital, where she had two kidney operations. Now, three years later, she has returned to her old haunts, living in a filthy crawl space between the train tracks and the wall. The stench of urine is unbearable. Captain Henry looks into the crypt, shines his light on the wool swaddled form. "Who is this?"

A woman says, "Go away, I'm sleepin'."

They talk, and she explains that she tried to get help from Connections, a Metro-North outreach office, but that she was offended by the "attitude" of an employee and gave up. Captain Henry says he understands, but adds: "You are literally sleeping in garbage. Do you realise this? Are you crazy?"

Then comes a signal, and Captain Henry and I have to jump into Brenda's den, flattening ourselves against the wall to let a long train pass. A terrible rusty, metallic squeal deafens us as the train passes by. The conductor waves at Captain Henry, who waves back. We are engulfed in the smell of rats, damp, urine and faeces.

When the train passes, Captain Henry tells Brenda about the rape of a friend of hers, underground, then he points up above, and I notice for the first time the far-off sound of footsteps on the pavement, pattering overhead.

"You hear that sound?" he asks Brenda. "That's the world going by. You know what your life is like? It's like being dead." She raises her head out of her blanket. "Just check this out right here," he tells her, pointing at her surroundings. "This is your grave. This transformer case above your head is your tombstone. Go out and get help. Do you want to live like this forever?"

"I will go to Connections," she says. "Wait. I have to get dressed."

Once.Brenda is dressed, we all head back above ground. As we walk out of dark train tunnel, on to the platform for Metro-North, she beams and squints in the light. I see a very attractive woman, with cornrowed pigtails and a broad face. She is carefully using strawberry lip balm, in preparation for the world above. It is hard in the daylight to believe that the woman we had found, burrowed like a worm in garbage, huddled in a urine-soaked nest of newspapers, is this very nomal-seeming person.

"I'm Brenda," she tells me. "I'm 30. I have three kids. They're with my mother. Me and her don't get along, even when I'm doing good. Last time I saw them was two years ago. I'm hungry."

On the street, Captain Henry buys her a fried egg and bacon sandwich on a roll. It's 9.15am, and Manhattan has one less Moleman today.

8 'Subway Cops and the Mole Kings', Channel 4, Saturday 9 March