He retraced his steps to the church where, to his annoyance, he found that Walter had been watching him. The red-headed woman was being led away and he spoke loudly so that she might hear. 'What time do you call this, then?'

'I don't know the time, sir. I was told to collect you.' Walter seemed very pale in the early morning light. 'I was told you were going to the Incident Room.'

Thank you for telling me.' And as they drove to Spitalfields Walter turned the radio to the conventional police wavelength, but Hawksmoor leaned forward and shifted the dial. Too many stories,' he said.

'Is it the same man, sir?'

'It's the same MO.' Hawksmoor emphasised the last two letters, and Walter laughed. 'But I don't want to talk about it yet. Give me time.'

The music of a popular song now came from the radio as Hawks-moor gazed out of the window; and he saw a door closing, a boy dropping a coin in the street, a woman turning her head, a man calling. For a moment he wondered why such things were occurring now: could it be that the world sprang up around him only as he invented it second by second and that, like a dream, it faded into the darkness from which it had come as soon as he moved forward? But then he understood that these things were real: they would never cease to occur and they would always be the same, as familiar and as ever-renewed as the tears which he had just seen on the woman's face.

Walter was now preoccupied with another subject: 'Do you believe in ghosts, sir?' he was saying as Hawksmoor stared gloomily out of the window.

'Ghosts?'

'Yes, you know, ghosts, spirits.' After a pause he continued. 'I only ask because of those old churches. They're so, well, old.'

There are no ghosts, Walter.' He leaned forward to turn off the song on the radio and then he added, with a sigh, 'We live in a rational society'.

Walter glanced at him: 'You sound a bit frail, sir, if you don't mind my saying'.

Hawksmoor was surprised, since he did not realise that he sounded like anything. 'I'm just tired,' he said.

By the time they had reached the Incident Room at Spitalfields, from where all the enquiries on these murders were still being so- ordinated, the telephones were ringing constantly and a number of uniformed and plain clothes officers were moving about the room, calling and joking to one another. Their presence unnerved Hawksmoor; he wanted nothing to happen until he understood the reasons for its happening, and he knew that he would quickly have to dominate this investigation before it ran out of control. A video unit was being placed in a corner of the room, and Hawksmoor stood in front of it in order to speak. 'Ladies and gentlemen,' he said very loudly. Their noises ceased and as they looked towards him he felt quite calm. 'Ladies and gentlemen, you will be working in three shifts, with an incident officer in charge of each shift. And there will be a conference each day -' He paused for an instant as the lights flickered.

'It has often been said that the more unusual the murder the easier it is to solve, but this is a theory I don't believe. Nothing is easy, nothing is simple, and you should think of your investigations as a complicated experiment: look at what remains constant and look at what changes, ask the right questions and don't be afraid of wrong answers, and above all rely on observation and rely on experience. Only legitimate deductions can give any direction to our enquiry.' A policewoman was now testing the video equipment which was being installed and, as Hawksmoor spoke, pictures from the various scenes of the murders -Spitalfields, Limehouse, Wapping and now Lombard Street -were appearing on the screen behind him so that momentarily he was in silhouette against the images of the churches. 'You see,' he was saying, The propensity for murder exists in almost everyone, and you can tell a great deal about the killer from the kind of death he inflicts: an eager person will kill in a hurried manner, a tentative person will do it more slowly. A doctor will use drugs, a workman a wrench or shovel, and you must ask yourselves in this case: what kind of man murders quickly and with his bare hands? And you must remember, too, the sequence of actions which follows the murder: most killers are stunned by their action. They sweat; sometimes they become very hungry or thirsty; many of them lose control of their bowels at the moment of death, just as their victims do. Our murderer has done none of these things: he has left no sweat, no shit, no prints. But one thing remains the same. Murderers will try and recall the sequence of events: they will remember exactly what they did just before and just after -' And at this point Hawksmoor always assisted them, since he liked to be entrusted with the secrets of those who had opened the door and crossed the threshold. He spoke gently and even hesitantly to them, so that they knew he was not judging them. He did not want them to falter in their testimony but to walk slowly towards him; then he might embrace them, in the knowledge they both now shared, and in embracing them despatch them to their fate. And when, after all the signs of fear and guilt, they confessed, he felt envious of them. He envied them the fact that they could leave him joyfully. '-But they can never remember the actual moment of killing. The murderer always forgets that, and that is why he will always leave a clue. And that, ladies and gentlemen, is what we are looking for. Some people say that the crime which cannot be solved has yet to be invented. But who knows? Perhaps this will be the first. Thank you.' And he stood very still as the incident officer for that morning arranged the men and women into various teams. A cat, adopted as a mascot, was accidentally kicked during these activities and ran screeching out of the room, brushing against Hawksmoor's right leg as he walked over to Walter who was now staring at the keys of a computer.

Walter sensed him at his shoulder: 'I don't know how you managed without them, sir,' he said without turning around, 'In the past, I mean.' After a noise which was as faint and yet to Hawksmoor as disquieting as a human pulse, certain letters and digits moved across the small screen. Walter now looked up at him in his eagerness: 'Do you see how it's all been organised? It's all so simple!'

'I seem to have heard that somewhere before,' Hawksmoor replied as he bent forward to look at the names and addresses of those convicted or suspected of similar crimes; and of those who had used a similar modus operandi -manual strangulation, with the murderer sitting or kneeling on the body of the victim.

'But it's much more efficient, sir. Think of all the agony it saves us!'

He now entered a different command, although his hands barely seemed to move across the keyboard. And yet despite his excitement it seemed to Walter that the computer itself only partly reflected the order and lucidity to which he aspired -that the composition of these little green digits, glowing slightly even in the morning light, barely hinted at the infinite calculability of the world outside. And how bright that world now seemed to him, as a face formed in an 'identikit' composition, flickering upon the screen with green shading in place of shadow so that it resembled a child's drawing. 'Ah,' Hawksmoor said, 'the green man did it.'

And when he grew bored with all this information, he decided that it was time to return to St Mary Woolnoth and resume the investigation there. It was almost midday when they reached it, and the autumn sun had changed the structure of the church so that once more it seemed quite strange to him. He and Walter were walking around to the side facing King William Street, when for the first time he noticed that there was a gap between the back of the church and the next building -an open patch of ground, part of which was covered with transparent sheeting. Hawksmoor looked down at the exposed soil and then drew back. 'I suppose,' he said, 'these are the excavations?'