'It's Walter.'

'Well then, Walter, tell me a bit more about yourself.'

'Well, like I told you, I work with him upstairs.' And both of them now looked up at the ceiling, as if Hawksmoor might even then have his ear to the floor. 'Previously I was with computers.'

Mrs West settled herself comfortably in her chair. 'Now that's a subject I don't understand. Like my thermostat.'

'It's simple. You feed in the information and out comes the answer.'

Walter never tired of this subject, although his eagerness seemed to exhaust Mrs West. 'You know, you could put the whole of London in the charge of one computer and the crime would go right down. The computer would know where it was going to happen!'

'Well that's news to me, Walter. And how does this computer know what to do?'

'It's got a memory bank.'

'A memory bank. Now that's the first time I've heard about anything like that.' She shifted in her seat. 'What kind of memory?'

The memory of everything.'

'And what does this memory do?'

'It makes the world a safer place.'

'Pull the other one!' she said as she lifted her skirt slightly and kicked her leg in the air. Her curiosity now sated, she moved over to the television and switched it on; and in companionable silence they both settled down to watch the cartoons which had appeared on the screen. Mrs West shrieked with laughter at the antics of a wolf and the little creatures it was pursuing; even Walter found himself amused by the inhabitants of this harmless world. But when the cartoon was over she gazed out of the window.

Walter rose to leave: 'It doesn't look as if he's coming back, does it?'

Mrs West shook her head. 'No he's out again for the night if I know him.' And Walter wondered what she meant. 'You can come again,' she said as he left the flat. Then she went to her window and watched him as he walked away, her hands drumming against her sides.

And it was not long after that Hawksmoor returned. When he opened the door of his flat, the full weariness of the evening hit him: he longed for sleep, since there was something screaming within him which needed to be laid to rest. The lights of Grape Street were reflected in his dark room, and he had only just entered it when he shrank back in alarm: something was sitting, or crouching, in the corner. He turned on the light quickly, and saw that it was only a jacket he must have flung there. 'My second skin,' was the phrase which occurred to him, and he repeated it softly to himself as he prepared for sleep. Then he dreamed, as others do, although he had learned how to forget his dreams.

The next morning he was sitting in his office, his back to the light, when Walter came in whistling. 'Don't you knock,' he asked, 'before you walk in?'

Walter paused until he saw that he was smiling. 'I called at your flat last night, sir, to tell you the news.' For some reason Hawksmoor blushed but, since he said nothing, Walter continued -although more hesitantly than before. 'It's as we expected, sir.' He laid some papers down on Hawksmoor's desk. The only blood and tissue groups were from the victim. Nothing at all off the other one, the assailant.'

'And did the other one leave no prints or marks?'

'As I said, nothing at all.'

'Doesn't that strike you as odd?'

'It's unusual, sir.'

'Good thinking, Walter.' Hawksmoor put on his glasses and pretended to examine the papers which Walter had brought to him. 'I want you to type out a report for me,' he said at last, 'and I want you to address it to the Assistant Commissioner. Put in all the usual details date and time of discovery, list of responsible officers, you know what I mean.' He leaned back and took off his glasses: 'And now, Walter, I will give you the facts as I understand them'.

And these were the facts, as far as anybody understood them at this time. On the evening of November 17 in the previous year, the body of a boy later to be identified as Thomas Hill, who had been missing from his home in Eagle Street for seven days, was discovered in one of the passages of the abandoned tunnel by Christ Church, Spitalfields: he had been strangled, apparently by hand since there were no ligature marks around the neck; and several ribs were broken which, with internal bruising, suggested that he had fallen from a height of at least thirty feet. Despite the most exhaustive examination, however, no trace of his murderer had yet been found -certainly no print marks, and no particles of the killer's clothes, were discovered anywhere in the vicinity. A thorough search of the grounds and of the tunnel had revealed nothing but a bus-ticket, and some pages torn from one of the many religious pamphlets on sale in the church itself: no significance could be attached to any of these items. House-to-house enquiries had been equally unsuccessful and, although certain suspects had been closely questioned, no real evidence of guilt was forthcoming. Then on May 30 of this year a vagrant known as 'Ned', but whose real name was Edward Robinson, was found by the door of the crypt beneath S t Anne's Limehouse; it was assumed at first that in a drunken stupor he had fallen down the steep flight of steps which lead to the crypt, but forensic examination revealed that he had been strangled -again no trace of the murderer was found upon the tramp or in the surrounding grounds. The only possible clue to the killer's identity was a photograph, very badly creased and damaged but apparently that of a small child, which had been found in a pocket of the vagrant's overcoat.

There was no reason to connect this killing with the murder of Thomas Hill six months previously, and in fact it might have been safe to assume that Edward Robinson had been a victim of one of the innumerable and often violent quarrels which break out between those inhabitants of the area known to the police as 'transients'.

Exhaustive questioning, however, had revealed no evidence of a fight or quarrel. The absence of prints or saliva upon the dead man had once more baffled the forensic scientist, and it was he who eventually surmised that there was a 'comparability factor' between the two cases. And then on August 12 of this year the body of a small boy, Dan Dee, was discovered in the ground behind St George's-inthe-East, Wapping. It transpired that the victim had left his house in Old Gravel Lane around six the previous evening in order to join his friends in a game of football beside the Tower Hamlets Estate; when he had not returned by eleven, his anxious parents contacted the police but it was not until the following morning that a constable had found the child's corpse lying beside an abandoned shelter in the grounds of the church. He had been strangled, apparently by manual means, but again no prints were found on the neck or body. House-to-house enquiries, a thorough search of the grounds, and exhaustive forensic tests had revealed nothing: an unhappy fact which Hawksmoor now added to the end of his report.

He could not help smiling as he recounted the details of these murders, and by the time he had finished he felt quite calm. 'So you see, Walter,' he said in a lower tone now, 'We live in the shadow of great events'. And then he added: 'If only we knew what they were.'

'He must be a madman, sir, mustn't he?'

Hawksmoor looked down at his hands, placed flat upon the desk: 'Don't assume that.'

'But I can assume he's dirt!'

'But the dirt needs the cleaner and the cleaner needs the dirt.' He drummed the fingers of his right hand on the desk. 'And tell me, Walter, tell me what else you think.'

'You mean, what do I think is the story?'

'We have to assume there is a story, otherwise we won't find him, will we?' His hand was still once more.

'It's difficult to know where to begin, sir.'

'Yes, the beginning is the tricky part. But perhaps there is no beginning, perhaps we can't look that far back.' He got up from his desk and went over to the window, from where he could see a thin pillar of smoke rising into the clouds. 'I never know where anything comes from, Walter.'