Down to an open fire-door, before which Jimmy stopped and looked round, nervously it seemed. Hayden smiled encouragingly, then realised he was still wearing the face mask. “You come please,” said Jimmy, holding wide the door.

The corridor beyond was disturbingly dark, lit only by a crack of greenish light that shone through a door left ajar at the further end. It didn’t look like normal room-lighting; Hayden was put in mind of the luminosity of certain sea creatures, or weird electrical discharges like Saint Elmo’s fire. Jimmy jogged down the corridor and gave a sharp double knock at the door, then vanished inside after signalling Hayden to wait.

Hayden heard voices through the open door, Jimmy’s first of all, then that of another, much older-sounding man. After a few seconds Jimmy reappeared. He positioned himself very close to Hayden and spoke almost directly into his ear.

“Doctor has agree to see you. Make—examination! Ready in a little while.”

“That’s good,” said Hayden uneasily. The subterranean consultant will see you now. They waited by the door, during which time Jimmy played a game of Tetris on his mobile phone. In the absence of chairs and magazines in this unorthodox waiting room, Hayden got bored; he made as if to take a look inside, but was blocked off rapidly by Jimmy. “Wait one minute!”

Frustrated, Hayden gestured with his hands at the bare corridor; Jimmy shrugged, I don’t make the rules round here. But even as he spoke, a guttural word of command came from inside the room, and Jimmy clapped his hands in satisfaction. Taking Hayden by the shoulders, he propelled him through the doorway. “See you outside,” he said, and vanished.

What had Hayden been expecting? Something stagey and traditional, a scene from the movies: a whiff of the mysterious East. An old-fashioned apothecary’s with boxes of dried frogs, incense on braziers and twirling paper lanterns; or a smoky Triad opium den, the lair of Fu Manchu. What he actually found himself in was something else again.

It was a plain concrete bunker, dank and claustrophobic, lined floor to ceiling with industrial slotted shelving. There were no light-fittings, nor were there any candles or lanterns. The only illumination came from an enormous fish-tank, which was lit partly by electric light, and partly by the eerie bioluminescence of whatever was inside it—Hayden couldn’t quite make it out, and wasn’t really sure he wanted to know anyway. Silhouetted against the greenly glowing tank was a figure, standing very close to the glass but facing Hayden.

He’d sounded like an elderly man, but looking at him now he could have been any age. Between the green medical cap and a face-mask like Hayden’s own hardly any of his features were exposed, and over his eyes he wore tinted swimmer’s goggles. The rest of his uniform consisted of a green smock and dark trousers, terminating an inch or so above his rope sandals; old man’s ankles, noted Hayden, glad to have something to cling on to. The overall effect was deeply unsettling, and probably only a man in Hayden’s sort of pain would have dreamed of going through with it. But he was desperate, and he wanted more than anything to get it over with, so he advanced a couple of steps into the room and bowed slightly.

The doctor said something brusque and croaky. Hayden thought of fetching Jimmy in to translate, then remembered that rolled up in his coat pocket was the invaluable copy of Scientific American. Bowing once more, he held out the magazine, indicating the article in question. The doctor made no attempt to look at it. Hayden gestured again for him to take it; this time the doctor extended a rubber-gloved hand and snatched the magazine away. He studied it for a minute, then rolled it up very tight as if wringing a chicken’s neck. He stared at his patient blankly, waiting for him to acquire basic conversational Mandarin perhaps. Behind him, the air filtration unit in the tank bubbled softly.

Hayden had hoped the doctor would catch on sooner. What to do? Gingerly, he removed his face-mask, the better to articulate his wants. “Aaangh,” he said, mouth wide open, finger pointing inside to the source of all his misery. “Naad toos. Agh ong.” Surely the old codger could see what the matter was? “Bad tooth. That one.” Please.

The doctor unrolled the magazine, looked from the article to the inside of Hayden’s mouth and back again. He traced his finger along the text and read aloud, “Den-tee-shon . . . denteeshon?” He looked back up at Hayden. Hayden nodded his encouragement. “Denteeshon,’”the old man repeated pugnaciously. Again Hayden nodded. The doctor spread his hands wide in the universal mime for no idea, and threw the magazine at Hayden’s feet.

Hayden scowled, then winced as his wrecked tooth yanked on its taproot of agony. How difficult was this going to be? “Look, I’ve got a toothache,” he said, speaking slowly and emphasising words as if clarity alone would render them comprehensible to the doctor. To drive the point home, he pulled back his lips from his teeth to reveal the offending molar. “Hajg hju—” the doctor recoiled as if offended, and Hayden removed his fingers from his mouth—“Have you got any of this stuff?” He tapped the headline, ran his saliva-smeared finger beneath the familiar words, words that now only mocked him: “MIRACLE” CHINESE DENTAL TREATMENT. The old man shrugged, and Hayden felt like picking him up, all six stone of him, and shaking him till the medication fell out. Why couldn’t everyone speak English, for God’s sake?

On the verge of giving up and going back to the hotel, he tried one more time. “Jimmy, the man who brought me here? He said you’d be able to get me treatment for it. Like in the magazine?” Pointing at the Scientific American on the floor. “He called it wan-chang something . . . wang-shan-dole?”

Behind the face-mask came a sharp hiss of indrawn breath. The doctor had understood that part, all right. Emboldened, Hayden repeated it, pointing at his tooth: “Wang-shan-dole?” He smiled, hoping at last to get the consultation properly under way.

Quaveringly, the old man pointed at him, and fired off a breathy burst of Cantonese; something fast and high and wildly inflected. It ended in uuan-shan-dhol and a question mark, and a finger insistently jabbed in Hayden’s direction.

Hayden seized eagerly on the one thing he thought he recognised. “Wan-shan-dole,” he assented, pointing at himself.

Even under his mask there was something almost comically incredulous in the doctor’s attitude—what, you?—as he let off another volley of Cantonese, again with that magic uuan-shan-dhol tucked away in it. Before Hayden could agree with him, the doctor was off and rooting through his shelves.

Without turning to Hayden he kept up a running commentary out of the corner of his mouth, shaking his head and throwing in the odd uuan-shan-dhol for good measure. At the time, Hayden was too impatient to register subtleties, but looking back later he got the feeling the old man didn’t really care to have him in the room much longer than was absolutely necessary, now he’d diagnosed the problem.

After all that fuss, it took the doctor less than a minute to come up with the goods: a pocket-sized cardboard box completely covered with small print in Pinyin and Standard Script. He held it out at arm’s length; Hayden went to take it from him, and had to grab it as it fell. The old man had simply let it drop, before snatching his hand away as if afraid of catching Hayden’s toothache.

Hayden turned the box round and round. “That’s great,” he said, hardly daring to believe he had the miracle cure in his hands at last. “Absolutely brilliant. How much do I owe you?” He took out his wallet and held it invitingly open.

The doctor, more animated and seemingly more nervous than before, scuttled forward and plucked out a few bills at random. Looking at what was left, Hayden realised he’d taken forty, fifty HK at most. The larger notes he’d withdrawn specially from the cash dispenser in the hotel lobby remained untouched. “Here,” he urged, taking out one of the hundreds and waving it at him, “that’s for your trouble,” but the doctor wasn’t having any. Backing away from Hayden, he jabbed a finger at the door and hit him with one last volley of croaky Yue dialect. Then he turned to the monster aquarium behind him. The consultation was at an end.

Slipping the cardboard box into his inside pocket, Hayden headed for the corridor. At the door he paused and tried to say goodbye: the old man turned impatiently around, lifted his face mask to reveal a flaccid maw lined with spiderish old-man’s beard, and spat on the bare concrete floor at his feet. That seemed final enough: Hayden left him to his fishing.

Jimmy was practically jogging on the spot with nervous excitement. “Come on now! Time—to go!” Hayden had to hurry after him up the stairs and back outside. They barged down the alleyways to the main street, Hayden feeling oddly like a john might feel on being dismissed from some tart’s parlour: surplus to requirements, something embarrassing to be got out of the way before the next punter showed up. At the taxi rank, Jimmy shook his hand for an unnaturally long time before relieving him of some of the high-denomination notes the doctor had spurned earlier. Once in the cab, Hayden couldn’t wait; hands trembling ever so slightly, he reached into his pocket for the box with the medicine in it.

“So,” said Dr. Pang, his face rigid in barely-concealed disapproval, “you self-medicated with this black market treatment?”