‘What’s that?’ Atkins was leaning out of the alcove to look at him as he came in the doorway; another head appeared, this one Maude’s; then, at knee level, the angular muzzle of the dog.

‘I wash my hands of the whole damned lot!’ Denton shouted.

‘Good enough for Pontius Pilate, should be good enough for you, Major.’

Atkins’s voice changed to a martial bellow as he began to order Maude about. Apparently the cleanliness of the alcove hadn’t been to his liking. After explaining that he didn’t give two hatpins whether Maude thought that cleaning was part of his job or not, Atkins said something disparaging about servants who thought they were too genteel to get their hands dirty; then he leaned into the sitting room again and said, ‘There’s mail for you.’ His voice took on a hectoring tone. ‘More bills, I’m sure.’

‘I wash my hands of them, too.’

‘Oh, no you don’t!’ Atkins came down towards him; Rupert padded behind, panting like a blacksmith’s bellows. ‘You neglect the bills, I’m on my way to the agent’s for a new position.’ He stood beside Denton’s chair, quite unembarrassed now by the hat’s sitting on the bandage, the Indian robe. ‘You wash your hands of Mulcahy and the dead tart, all well and good; best get to work on that book, then.’

‘You’re as good as a mother-in-law.’ Denton was opening bills and putting them with others he hadn’t paid. Soon, he’d have to write apologetic letters and ask for time. Bad. He opened a plain one that looked like a begging letter - he got those now and then; people thought writers were rich - and took out a note of a different size, scrawled in an almost illegible hand. It was from the woman he’d visited, Mrs Striker: he could talk with three young women if he would come to her office at five o’clock on the second.

Today was the second. It was barely two.

Telling himself No, I’m done with it, done with all of them, he slit another envelope with a finger without looking at its origin and realized only when he held the contents in his hand that it was from his typewriter and that the women she’d hired must have found more Mulcahys in the directories. More expense. With it was a mere phrase scribbled on a blank sheet - ‘As promised, the names from the adverts’ - and her bill. He crumpled that before Atkins could see it but couldn’t keep his own eyes from going to the total, which was startling.

‘Oh, no,’ Atkins said, reading over his shoulder. ‘Not more Mulcahy! Send it off to that copper, Guillam.’

‘Never again.’

‘You just said you’ve washed your hands of Mulcahy - didn’t you? You did; I heard it with my own ears. You’re done with Mulcahy!’

‘I’m more done with Guillam. I wouldn’t send him my old drawers.’ He was looking at the new list Mrs Johnson had sent. Only seven addresses, all businesses; four were far from the metropolitan centre, all suburban shops that seemed to offer him nothing. Of three closer in, one was a Regina Mulcahy, Fine Linens - not likely; one was a Richard Mulcahy, Processed Beverages, the Famous So-Do-Pep, Health Drinks for the Health Conscious - possible, but nothing leapt out at him; and one was a Regis Mulcahy, Now Proprietor of the Photographic Inventorium, Under New Management, the Famous Periscopic Lens, Patent Applied For. ‘Photography!’ he said.

‘Wash your hands of it, General!’

‘A camera, Atkins! That’s what he could have left behind in the closet - a camera! And that’s why the murderer went after him - he thought Mulcahy had taken a photo of him and had run out with the plate. And maybe he had! My God, no wonder Mulcahy was terrified!’

‘You’re making it up, General!’

‘It fits.’

‘You’re writing fiction. Go make money off of it.’

‘It all fits, damn it!’

‘I’ll have fits if we don’t pay some of those bills!’

Denton turned on him and was ready to say something ugly, but he was stopped by Atkins’s ridiculous costume and his ridiculous dog. He grunted, shook his head, said, ‘I’m going out.’

‘Oh, no - no, don’t, Captain! Bloody hell, you’ll be in it up to your elbows again!’

‘Just this once.’

Atkins groaned, but Denton was already grabbing up his mackintosh and hat. He grinned. ‘Don’t wait up.’

Atkins met him at the downstairs door with the overcoat he’d been working on. ‘You can’t wear a mac on a day like this - what would people say? Take it off.’ He took the Colt from Denton and demonstrated his handiwork: the revolver’s barrel slipped through a hole into the overcoat’s lining; a kind of envelope of canvas-lined tweed held it upright, the grip ready to the hand.

‘Ingenious,’ Denton said. He put the coat on. The pistol’s weight dragged it down on the right side, but he could draw the weapon easily without having to fumble for it as he had before. ‘And it’s practically invisible,’ he said.

‘It’s invisible the way Nellie’s mistake’s invisible in about the sixth month, General, but it’s better than it was and you’re not an embarrassment to me going out in it. Though I say again, you ought to be filling the coffers and not chasing will-o’-the-wisps.’

Denton put a fingertip on Atkins’s shoulder. ‘Was it a will-o’-the-wisp that put that turban on your head?’ He withdrew the finger. ‘Expect me when you see me.’

If the neighbourhood had ever been up, it had come down; lower houses on each side had weeds where there might once have been grass, broken windows stuffed with rag or filled with paper. From somewhere behind the street, the sound of a machine thudded, and there was a faintly chemical smell. Denton went close to the building on one side, trying to look along it, but a tall wooden gate closed off the narrow space between it and the next house. Looking in through a crack, he could see only weeds, in a space the sun never touched.

He went up the three steps to the central door. On one side, the remains of a stone urn, in which torches had long ago been extinguished, remained; the other had been tipped down into the lower entry, where it lay in pieces among smashed bottles and weeds. The door was open; through it, the thudding noise was louder, rather menacing, and the chemical smell was strong. Denton stepped inside. Straight ahead was a stairway, and beyond it another door, also open; through it, he could see part of a yard and a wooden building. To his right, a door was closed; that was the side where the windows had been bricked up. To his left, a large opening showed where a wall had been pulled out; three men, stripped to the waist, were working over vats of poisonously coloured liquid in there.

Denton walked to the back. The yard was littered with metal castings and wooden boxes; at one side, a workman was hammering sand into one of the boxes. Denton knew enough of manufacturing to see that the box was a mould; the workman was preparing a sand casting. The foundry, he guessed, was still farther back.

He went in again and looked into the big room with the vats. Two of the men were lowering a casting into a vat with a chain hoist. Plating, he thought. Or cleaning. He tried to get the attention of the third man but was ignored; maybe it was the noise of the thudding, ponderous machine, probably a drop forge but sounding like the footsteps of a monster.

Finding no sign to tell him where the Photographic Inventorium might be, he went up another storey. Here, a single door on the left opened on a space the length of the house, undoubtedly made from two or even three old rooms - the cornice changed halfway down; a ragged scar ran across the floor where a wall had been removed. Far down the room, a dark man in a skullcap stood on a small dais, a kind of counter around him. The rest of the room was bins, both along the walls and down the middle. While Denton watched, a young man rummaged in a bin, pulling out bits of lace, studying them, picking out one or two and dropping them into a sack. When Denton moved deeper into the room, he saw a sign behind the dais: A. Gold: Findings, Trimmings and Best Remnants.

‘Mr Gold?’

The man on the dais folded his arms over his chest, cocked an eyebrow. Standing up there gave him an advantage, and he was aware of it. ‘So?’ he said.

‘I’m looking for something called the Photographic Inventorium.’

Gold pointed skyward.

‘You know the man who operates it?’

Gold shook his head.

‘Have you seen him in the last few days?’

Gold shook his head.

‘Thanks.’

Denton went up to the next floor. There, a young man who was planing panels for a door said he didn’t know Mulcahy and wouldn’t recognize him if he fell over him, and he’d seen only one person on the stairs in the last week, and he didn’t know him, either.

‘What’d he look like?’

‘Who wants to know?’

Denton offered a couple of shillings, glad Atkins wasn’t there to see him, and the young man said what did he think he was, a flunkey? ‘I’m a self-employed craftsman; I don’t take charity and I don’t take bribes. You see this here door I’m making? It takes skill. It’s hard work, and not many can do it. And nor can I if you won’t let me be!’ He turned his back and began to run a steel-bodied, rosewood-filled plane across the wood. Denton wanted to linger, the odour of the wood enticing, the artisan’s concentration impressive, but the young man gave him an angry look and he left.

The Photographic Inventorium, Under New Management - no mention of Mulcahy - was on the top floor. Two doors stood up there, silent and closed; the other, if it had an owner, bore no sign. The door to the Inventorium had two hasps, both locked with big Brahma padlocks. Denton knocked and waited and knocked again, but nobody came.

The Inventorium was closed.

The drop forge thudded. The cabinetmaker sawed a plank. Denton tried the other door and called out Mulcahy’s name, but the building, if it knew something, was dumb.

He was up in the part of the building, he thought, where the dormers projected from the steeply pitched hip roof. Yet the stairs, which had moved from the centre to the far side of the house on their way up, here broke off and, like a snake cut in two, continued in a different place. He found them only by prowling the corridor and seeing, right at the back, the walled-in stairway going up. If he was right about how high he had come, these stairs led to the roof.

He went up.

The stairs turned once and ended under a trapdoor that must, he thought, open in the almost flat part of the roof that covered the centre of the house. Denton could come within only four steps of it; even then, he had to duck his head. The trapdoor had been locked with a chain heavy enough to haul logs, and a padlock as big as his fist.

Which had been broken.

Denton felt his heart lurch. He looked at the lock, which hung from the chain as if still locked, perhaps arranged so that the casual eye would think it was. He put his eye close to it, his hands on the dirty stairs, his hat off. A gouged scar marked the inside of the lock’s curve, but he saw nothing to tell him when it had been made. The metal was dark with time, the gouged line hardly brighter. It could have been made months before. Or yesterday. He reached to take the lock out of the loops of chain, stopped himself, thinking of Guillam. Tampering with evidence. Would he even tell Guillam about any of it? Well, just in case— He took out the white handkerchief that Atkins insisted he carry and removed the lock with the care of a man stealing an egg from under a hen. Then he used the handkerchief between his fingers and the trapdoor to push it open.

The trap must have weighed thirty pounds. He let it rest on his head and neck while he peered under it over the roof. Here, the roof was made of four triangles like pieces of a square pie that met in the centre; at their outer edges, the roof plunged into the steep decline he had seen from the street. Orienting himself, he turned his head towards the side where the Inventorium sat behind its locked door.

He made himself breathe slowly. He knew he was going to have to go out on the roof, and he was afraid of heights. But he would go out only to look. Only to look.

He lowered his head, letting the trap down; gloom closed in on the stairs. He laid his folded overcoat on the top stair, then put his hat - grey, American, soft and somewhat wide-brimmed - on top of it. He hesitated. It was early December, cold outside; the grey sky threatened wet snow. He decided against taking off his jacket. He breathed.

Unable to postpone things any longer, he raised the trap again and got ready to step out. Then, thinking that somebody (but who?) might put the broken padlock through the chains while he was on the roof, he used his handkerchief to slip the padlock into his pocket. Only later did it occur to him that anyone who wanted to lock him out need only loop the chains - no padlock needed. But it would be too late to go back by the time he had the thought.

He went up a step; his head rose above the roof, and he was able to look along the slight incline and beyond to the grey sky. Up another step, he could see housetops and chimney pots, and if he’d dared look that way, he could have seen the edge along the Inventorium where the roof plunged down its final dozen feet to the eave. He went up another step.

Edgar Allan Poe had written a story about the pull of an abyss on the onlooker, ‘The Imp of the Perverse’. That imp had tempted Denton all his life - on barn roofs, on cliffs, on the rail of a steamship. Now, it beckoned to him from the edge of the roof: Down here - come down - look over the edge, it’s lovely - take a step out into the void— His fear was not so much of heights as of the imp, and what he might make Denton do.

The central peak was to his left, the slope down towards the Inventorium’s edge to his right. Ahead - he didn’t dare turn his head yet - was the peak and then the panorama of London. Even dimmed by autumn mist, it seemed inhumanly large, the sky as huge a bowl as over Montana. Far off to his left was St Paul’s; nearer to his right, the sand-coloured bulk of St Pancras station, Euston beyond it; move the eyes a bit to the left, there was the British Museum. The Thames was there somewhere in the middle distance, hidden by buildings, but he could make out London Bridge and the clock tower at Westminster. Looking from a height at this distance, the depth of the house separating him from the void, he didn’t hear the imp.

He took a breath and went out. Not daring to stand out there, he sat down. He looked all the way around, the entire compass of London. The thudding of the machine was clear, but under it, around it, was a steady roar made of iron wheels on pavement, the scuffing of shoes, voices, music, hooves, the clatter of machinery - the city.

He would have to look at the Inventorium’s side of the building, which was the side, he was sure, where he had seen an open window. Only look.

He removed the black silk that served as a sling. He took off his shoes. His stockings were instantly wet from the slates, which were shiny from the mist and which had moss growing in their chinks.

He swung around with his feet pointing down the gentle slope and his heels trying to dig into the moss. The roof was slippery with condensation, but at intervals of a dozen feet or so iron prongs curled up like monkeys’ paws to support roofers’ or repairmen’s ladders. A few were broken off; all were rusty. Still, as he started to work his way down on his rump, he clutched one for as long as he could. It felt solid enough, as did another, and then one crumbled away in his hand, and his heart rate accelerated and he had to lie back with his head on the slates.

Come on, the Imp said, down here - just slide down and look over—

He started down again. His injured arm ached. He thought he must look like an inchworm, sliding his rump down until his knees pointed up, then straightening his legs and sliding again. His suit was being ruined. He didn’t look where he was going but used the lines of the slates as a guide, his face turned to the sky, until he felt a change under the backs of his calves and knew he’d reached the end of the easy part, and his feet were now sticking out over empty space. The imp was shouting with glee.

He told himself he couldn’t go any farther. He told himself he was too frightened to go farther.

He wished he’d taken his coat off, because he was running with sweat. He could feel it in his hair and trickling into his eyes. He breathed once and forced himself to look towards his feet.

He saw his own legs and shoeless feet, then empty air, London rooftops a distant background. His heart lurched. The next building was a storey shorter, but he could see its peak and part of its roof. It seemed far down. Down there, four storeys below, he thought, was the weedy gap he’d peeked at through the gate. Dizzied, he looked to his left: there was the roof he was lying on and, jutting from it, the triangular bulk of a dormer - if he was right, a dormer of the Photographic Inventorium.

Well, he had looked. He didn’t dare do more.

He brought his feet back and reversed the inchworm motion of coming down, pushing himself up several slates, palms slipping, then crab-crawled sideways until he could by reaching - heels braced, legs flat against the roof, back arched to keep his balance back - touch the beginning of the dormer.

Now.

He wouldn’t try to go down, but if he did, the worst part would come right at the beginning of the last descent, when he would have to put his feet on the sharp pitch downwards but couldn’t yet get a grip on the dormer eave. A glance told him that there was no gutter there, only a rotten soffit and eave and the slates, one of which was hanging out into space from a single nail.

Heart pounding, Denton inchwormed down. His buttocks reached the beginning of the sharp downslope. His palms, braced on the tiles, were just at the point of sliding. He told himself that he hadn’t committed himself yet; he wasn’t really going down there; the imp wasn’t tempting him—

He rolled on his belly. He put his feet down until toes felt slate, his torso and arms extended up the central, gentle slope, his right hand with a death grip on an iron monkey’s paw. He groped left and right with his toes, then up and down, looking for one of the iron supports, trying not to think of what he was doing - lowering himself to a seventy-degree pitch with no support. Sweat was running stingingly into his eyes; he tried to wipe it off on the moss that was pressed against his face. He swore.

His left foot found an iron paw. He pushed on it; it felt solid. He put more of his weight on it. Still solid. He looked to his right, twisting his neck, to locate the dormer. Three feet away. Could he put his weight on the iron support and still reach out for the dormer eave and—?

The iron support broke. Not slowly, not crumblingly like the other one, but like a snapped twig, and he slid off the central part of the roof. He was still twisted towards the dormer and he made a grab at it, actually touched the broken slate, but the slide was accelerating, and he tried to get on his back, not knowing why - what good would it do? - but down he went, fingers scrabbling at the slates, nails breaking, like a nightmare, the worst of nightmares realized: he was going over the edge and into the abyss.

The iron paws had been put up in lines at right angles to the eaves, so that one jutted up eight feet below the broken one. His foot caught it, slid over, and would have gone on except for his turn-up, which snagged and held - good British woollens. The paw sagged, bent, but held. He felt it, felt his direction change from a downward plunge to a swing as the turn-up became the centre of a circle on which his weight spun, throwing him down and to his right, closer to the dormer. He dug with his hands, his arms; he tried to force his chest into the slates; his injured arm felt a jolt like electricity as it took all his weight. His hands, swinging around, struck the side of the dormer and he slowed and stopped, his hands spread against the wood as if he were a suction-toed frog, held for as long as his trousers and his arms could hold out; and then there was nothing for it but to look down, terrified, down the steep slope to the vertical drop-off. Just short of the edge, another iron support jutted up, closer to the line of the dormer than his right foot, which had got within inches of the edge. He thought he could have hung there longer except for the pain that was burning up his injured arm and into his shoulder, now spreading over the top of his left arm towards his clavicle.

He moved the foot over and caught the iron paw. And then hung there. Listening to the imp.

He could see the dormer’s corner now; it rose in line with the building’s external wall, about eighteen inches from the edge of the roof. He was still two feet above the corner, his right foot six inches below it. He had either to move his left foot so as to put all his weight on the one support, or move his hands down the dormer wall until he could grasp something, perhaps a window ledge, to pull himself up.

The fingers of his right hand inched down the wall, palm flat against it. At the bottom, an irregular brick gave a kind of fingerhold. Then he inched his left foot off its support and moved his left leg over towards his right, finding it impossible to put both feet on the paw because he couldn’t get his left leg under his right, and then he was lying partly on his left side. Bending his legs, he let himself down the dormer and felt around the corner, up, then a few inches across the face, and at last to the sill of the open window.

He found a handhold in the windowsill, a blessed, blissful handhold, and he pulled his weight to the corner and then up, and then he could pull his right foot up and put the left foot briefly on the paw, and then he was sitting in the open window with his feet on the slates, his toes six inches from the edge of the roof.

Then he was going to be sick, and the imp was tempting him to be sick over the edge, and he scrambled through the window, his knees on the floor inside and his belly on the windowsill, and he bent forward, ready to vomit, his chin where his toes had been, almost at the edge. And he looked down, straight down into the void, and saw the black walls of the buildings like the sides of a funnel, and the strip of weeds at the bottom, and among them an unrecognizable dark shape like a twisted dark star.

He had found R. Mulcahy.