It was after the man in the bed next to him died, with a grisly rattling in the night, that Tyke Tierney began to decline. Before that, he'd been tirelessly cheerful and garrulous on the ward, even when told that his lung cancer was terminal and that he had, perhaps, no more than six months to live. The youngest of seven Belfast brothers, "Tyke" had always been the little guy whom everyone loved. His wife said he'd been behaving like a wee boy for 67 years - until now.

Overnight, Tyke changed. He stopped flirting with the nurses, waved the physios away. Suddenly, he was bitter. It was just his luck, he said, to be last in line to his brothers, and then to die first. His wife Angela was distraught. She had never heard him speak like this. He'd always considered himself lucky, getting out of Belfast, doing well enough for himself, finding a nice home in Holloway. All she could think to say was that maybe now, after all these years, he should see a priest. It didn't matter that he'd always been one of life's doubters. It was never too late.

"Aye, wouldn't that be just like me?" Tyke replied. "Back of the queue for the church as well. What would I say? Forgive me, Father, but it's been 50 fucking years since my last confession." After that outburst, he barely spoke.

When Tyke's name came up at the hospital's weekly management round, a nurse suggested he was depressed. Apart from the need for a drip, he was, medically speaking, ready to go home. The house officer duly made a note to call a psychiatrist and request an opinion.

At the nursing station, the young psychiatrist picked up Tyke's notes, feeling out of place in the bustle of a real hospital. He tried to concentrate. Thyroid levels, sometimes associated with depression, were normal. Tyke had been prescribed a range of drugs commonly given to the elderly, but there were none of the likely pharmacological culprits for low mood. The man was dying. He was depressed. So much for expert opinion.

It struck the psychiatrist that he was acting out a bleak medical comedy. "Mr Tierney," he imagined himself saying, "the intolerable prospect of death has lowered the serotonin levels in your nervous system, but we may be able to alleviate the problem with some antidepressants. Alternatively, we could offer cognitive therapy - help you reorient some of your negative beliefs. Would you like that?"

The old man was asleep when the young psychiatrist approached bed 17. As he pulled up a chair, Tyke woke up, his eyes cloudy. "Are you the priest?" he asked blearily. "No, Mr Tierney, I'm a psychiatrist. Your doctors wanted me to have a chat with you." "Oh, that's OK," Tyke said. "I thought Angie might have found one behind my back; got last rites in early. Very organised, my wife." "I take it you're not a believer?" "It's not that," Tyke said. "I just never gave it much thought. Didn't see the point."

Tyke gave no indication of being preoccupied about his own death, but repeatedly returned to the subject of the man who'd passed away in the bed next door. "Terrible noise, like someone was pulling the man out through his own throat. They'd filled his bed again by lunchtime."

The psychiatrist went to call Tyke's wife, to assess a bit of "collateral history". Whatever Tyke's faults had been, she said, he always made up for them with his optimism. Mrs Tierney's Belfast accent became more pronounced as she told him what she thought the problem was now. He'd always avoided religious talk, she said. "But he worried his head about it just the same, and now it's killing him as much as the cancer."

The young psychiatrist put down the phone and turned mechanically to the drug chart. He prescribed 20mg of Citalopram. An uptake of serotonin to replace a deficiency of belief? The man still had a bit of time left. If he was depressed, let him have an antidepressant. Would a priest have done any better? The psychiatrist was no more able to credit that idea than Tyke had been.

An older doctor approached, asking to look at the notes. He was one of the palliative care physicians and had also been asked for an opinion. How many opinions constitute a belief, the young psychiatrist wondered, facetiously. He told the palliative doctor about his conversations with Tyke and his wife. The older doctor nodded and smiled.

"I don't know much about psychiatry," he said, "but it's interesting what belief does to the dying. Or unbelief. The religious ones and the atheists generally do all right. But the people who can't make up their minds - the agnostics - they're the ones who really suffer."

· Names and details have been changed.