‘I hear you were married,’ said Mr Kwang, as they waited. ‘I should offer you my congratulations.’

‘Kwang Lee told you?’

‘I don’t recall. My informants are too numerous. I know everything that happens in Sacramento, in Napa, in Sonoma, in Oakland, almost as soon as the ferries dock. I deal in girls, Mr Edmonds, just as you deal in hardware, and I need all the intelligence I can get.’

The girl came back and handed Mr Kwang a small white bottle with a sealing-wax stopper. Mr Kwang passed it to Collis.

‘In that bottle is a strong tincture of opium,’ he said. ‘Be careful with it. Too much, and you may arrest the heart.’

Collis looked at the bottle for a moment and then slipped it into his coat pocket. ‘I’ll be careful.’

Mr Kwang smiled faintly. ‘You need not pay me now. But when you have successfully accomplished whatever you intend to do with that tincture, you may present me with a railroad flag as a souvenir.’

‘How do you know this has anything to do with the railroad?’

Mr Kwang picked up his brush. ‘You are getting yourself a reputation, Mr Edmonds. Everything you involve yourself in, no matter what it is, has something to do with the railroad.’

Collis looked steadily at Mr Kwang. A gong reverberated somewhere in the house, like a reminder of a far country and a long-lost life. Collis stood up, paused, bowed, and then turned to leave.

Mr Kwang said: ‘There is a Chinese saying, Mr Edmonds, which is almost impossible to translate. But the meaning of the words is that he who tries to buy the future can only do so at the expense of the past.’

Collis stopped for a moment by the bamboo curtain. ‘You’re a hard man, Mr Kwang,’ he replied. ‘Harder than I am, without a doubt. But give me time.’

He waited for an answer, but all he heard was the sudden rattle of the abacus. He pushed through the bamboo curtain, walked along the narrow balcony, and then went down the stone steps to the street.

His last call of the afternoon was on Pine Street, at the corner studio of W. P. Naylor, Ambrotypist & Photographer. It was a small, dusty place, crowded with tripods and rolls of background paper and smelling strongly of sodium hyposulphite. In the window, faded by the sun, were gilt-framed photographic portraits of W. L. Winn, one of the pioneers of the fashionable San Francisco soda fountain; and of a homely lady in a white dress who plainly fancied herself as Ophelia.

Collis went into the studio and pinged the brass bell on the counter. He waited for a while and then pinged it again. At length, there was a flurry of shuffling and cursing from the back of the premises, and a thin young man emerged, in rolled-up shirtsleeves and acid-stained vest, his spectacles perched amid his wild prematurely grey hair.

‘Yes?’ he snapped.