'You wanted an explanation, Calcutta,' Murugan said. 'That was the deal. And I'm going to give you an explanation, but I'm going to begin exactly where I want to.'

'And you want to begin at the P. G. Hospital?' she said.

'That's right,' he said. 'That's why I'm taking you there.' She noticed the taxi driver watching them in his mirror. She leaned over and waved her packet of fish under his nose. 'What're you looking at, you cabbage-head?' she snapped. 'Keep your eyes on the road.'

Chastened, the driver dropped his eyes.

'Wow!' said Murugan. 'What was that all about?'

'And you,' she cried, turning on him in fury. 'Who are you, exactly?' Suspicion was raging in her mind now; she began to recall all the stories she had heard about foreign con-men and kidnappers and prostitution rings in the Middle East. 'I want to know who you are and what you are doing in Calcutta. I want to see a passport.'

'I don't have my passport with me right this minute,' said Murugan. 'But you can have this.' He took out his wallet and handed her his ID card.

She looked it over carefully, examining the lettering and matching the photograph with his face.

When they reached the Rabindra Sadan auditorium, Murugan tapped the driver on the shoulder and pointed down the road. 'Over there,' he said. 'Stop, over there.'

'Here?' Urmila found herself looking at a brick wall, across a narrow ditch. 'Why here? There's nothing here; we've left the hospital entrance behind: it's over there.'

'We don't need the entrance,' said Murugan, handing the taxi driver a fifty-rupee note. 'There's something I want to show you right here.'

'But there's nothing to see here,' Urmila said suspiciously. 'It's just a wall.'

'Look over there,' said Murugan, counting his change.

He pointed over his shoulder at the memorial to Ronald Ross. 'Did you get an eyeful of that?'

Urmila's eyes widened in surprise as they followed his finger to the marble plaque at the apex of the modest little arch. 'No,' she said. 'I've never noticed it before.' She began reading aloud: '''In the small laboratory seventy yards to the southeast of this gate Surgeon-Major Ronald Ross I.M.S. in 1898 discovered the manner in which malaria is conveyed by mosquitoes.'''

She shook her head. 'It's strange,' she said. 'I've changed buses here hundreds of times. I can't even begin to count how often I've walked past this wall. But I've never noticed that inscription up there.'

'No one notices poor Ron any more,' said Murugan. He set off towards a gate a short distance down the road. 'Follow me,' he said, beckoning her on. 'I'll show you something else.'

A chain hung suspended from the gateposts, just loose enough to let one person through at a time. Murugan went first and when Urmila caught up he pointed across the hospital's busy compound to a graceful red-brick building set well back in the grounds.

'When Ronald Ross came to work here in 1898,' Murugan said, 'that building over there was all there was of the P.G. Hospital.'

'How do you know?' she said.

He laughed. 'It's simple,' he said. 'You happen to be speaking to the world's greatest living expert on Ronnie Ross.'

'You mean you?' she said.

'You said it.' He turned on his heel and set off down a path that was bustling with uniformed hospital staff.

'Look over there,' he said, pointing ahead at a complex of boxy new buildings all painted a drab, municipal yellow. 'None of those was here when Ronnie was doing his malaria research in Calcutta. It was just trees and bamboo and greenery around here – except for a couple of labs and outhouses where the servants and attendants lived.'

He held a handkerchief to his nose as they walked past an open rubbish dump where crows, dogs and vultures were fighting over scraps of food and blood-soaked bandages. Nearby, a row of men stood lined up against a wall, unheeding of a notice that pleaded: 'Please do not urine here.'

Murugan came to a halt in an open space, between two wards, one of which bore a sign, 'Ross Memorial Ward'. He pointed to an old-fashioned red-brick bungalow that had been incorporated into one of the hospital's newly added wings. 'Look over there,' he said. 'That was Ross's lab.'

He went over to the bungalow and drew her attention to a marble tablet, set high in the wall. The tablet bore a stylized image of a mosquito, and under it an inscription.

'It's too far up to read,' Urmila said. 'Doesn't it say that it was in this laboratory that Surgeon-Major Ronald Ross made the momentous discovery that malaria is conveyed by the bite of a mosquito?'

'Something like that,' said Murugan.

Urmila pulled a quizzical face. 'What a strange little building,' she said. 'It looks so shut in on itself. It's hard to believe that anybody could discover anything in there.'

'What's even harder to believe,' said Murugan, 'is that this was once one of the best-equipped research laboratories in the whole of the Indian subcontinent.'

'Was it?' she said, in surprise.

He nodded: 'That's right. And you know who set it up?'

'How would I know about that?' she snapped.

'But you do know,' said Murugan, 'as a matter of fact, you've got his name right there.' He pointed at the piece of paper that she had tucked into her blouse.

Turning her back to him, she took the ball of paper out of her blouse. 'Here it is,' she said. 'Show me.'

He pointed to one of the lines that had been marked in ink. 'That's him. Surgeon-Colonel D. D. Cunningham.

'That's the guy who set up this place,' said Murugan. 'Like Ronnie Ross he was a doctor in the Indian Medical Service, which was a unit of the British Indian Army. But Cunningham was more or less a senior citizen, years older than Ross. And he was a research scientist too – a pathologist. In fact he was a Fellow of the Royal Society; he had an FRS tagged to his name, which was one of the fanciest tags you could get those days. Cunningham did a lot of his work in Calcutta right here in this lab. He made it into the best equipped research centre in this part of the world. It was Ron who made it famous, but he couldn't have done it without old D. D. '

'I'll take your word for it,' said Urmila. 'But I still don't see how this makes those papers so special.'

'Patience, Calcutta,' Murugan said. 'I'm just getting started. Come on.'

He headed back the way they had come and led her through a passageway to the narrow dirt-filled space that separated the Ross Memorial Ward from the hospital's boundary wall. The memorial arch was now a few yards to their left, and over the top of the wall they could just see the clogged traffic on Lower Circular Road.

Murugan pointed to a couple of low, ramshackle tinroofed structures, nestling in the mounds of earth and debris that were piled up against the wall. 'You see those outhouses over there?' he said. 'That's where Ronnie Ross's servants lived. One of them, a guy called Lutchman, was Ross's right-hand man. He used to breed the pigeons that Ross used for his research right over there.'

'Pigeons?' said Urmila distractedly, casting a distasteful glance at the little heaps of excrement that lay half-hidden in the debris. 'I thought you said he was working with mosquitoes and malaria.'

'Well, let me put it like this,' said Murugan. 'Ronnie Ross didn't always work with your usual plain-vanilla kinds of malaria. In Calcutta he began working with a related avian species, halteridium – you could call it a bird version of malaria.'

'Really?' Urmila looked up warily at the trees around them.

'Yes,' he said. 'And to keep him supplied with material for his experiments, his assistants, Lutchman and his crew, kept a large flock of infected birds – right over there. And they released their entire flock here, in September 1898, just days after Ross finished his final series of experiments.'