'What knife?'

'Two knives, actually.' I paused. 'One has a handle of polished striped wood that I think may be rosewood. It has a black hilt and a black double-edged blade an inch wide and almost six inches long.'

'A black black blade?' blade?'

I confirmed it. 'It's a strong, purposeful and good looking weapon. Would you know it from that description?'

He put his empty cup carefully on his desk and took mine also.

He said, 'The best-known black-bladed knife is the British commando knife. Useful for killing sentries on dark nights.'

I nearly said 'wow' again, not so much at the content of what he said, but at his acceptance that the purpose of such knives was death.

'They usually come in olive-khaki webbing sheaths,' he said, 'with a slot for a belt and cords for tying the bottom of the sheath round the leg.'

'The one I saw had no sheath,' I said.

'Pity. Was it authentic, or a replica?'

'I don't know.'

'Where did you see it?'

'It was given to me, in a box. I don't know who gave it, but I know where it is. I'll look for "Made in Taiwan".'

'There were thousands made in World War Two, but they are collectors' items now. And, of course, in Britain one can no longer buy, sell, advertise or even give such knives since the Criminal Justice Act of 1988. A collection can be confiscated. No one who owns a collection will have it on display these days.'

'Really?'

He smiled dimly at my surprise. 'Where have you been, young man?'

'I live in California.'

'Ah. That explains it. Knives of all sorts are legal in the United States. Over there, they have clubs for aficionados, and monthly magazines, and shops and shows, and also one can buy almost any knife by mail order. Here, it is illegal to make or import any knife with a point where the blade has two cutting edges and is over three inches long.' He paused. 'I would guess that both the trench knife the police showed me, and your putative commando knife, came here illegally from America.'

I waited a few seconds, thinking things over, and then said, 'I'd like to draw another knife for you, if you have a piece of paper.'

He provided a notepad and I drew the Fury, giving it its name.

Derry looked at the drawing in ominous stillness, finally saying, 'Where did you see this?'

'In England.'

'Who owns it?'

'I don't know,' I said. 'I hoped you might.'

'No, I don't. As I said, anyone who owns such a thing in Britain keeps it invisible and secret.'

I sighed. I'd hoped much from Professor Derry.

'The knife you've drawn,' he said, 'is called the Armadillo. Fury is the manufacturer's mark. It's made of stainless steel in j.a.pan. It is expensive, heavy and infinitely sharp and dangerous.'

'Mm.'

After a silence, I said, 'Professor, what sort of person likes to own such knives, even in secret? Or, perhaps, particularly in secret?'

'Almost anyone,' he said. 'It's easy to buy this knife in the United States. There are hundreds of thousands of knife buffs in the world. People collect guns, they collect knives, they like the feeling of power...' His voice faded on the edge of personal revelation and he looked down at the drawing as if unwilling for me to see his eyes.

'Do you,' I asked carefully, without inflection, 'own a collection? A collection left over, perhaps, from when it was legal?'

'You can't ask that,' he said.

A silence.

'The Armadillo,' he said, 'comes in a heavy black leather protective sheath with a b.u.t.ton closure. The sheath is intended to be worn on a belt.'

'The one I saw had no sheath.'

'It isn't safe, let alone legal, to carry it without a sheath.'

'I don't think safety was of prime importance.'

'You talk in riddles, young man.'

'So do you, Professor. The subject is one of innuendo and mistrust.'

'I don't know that you wouldn't go to the police.'

'And I,' I said, 'don't know that you wouldn't.'

Another silence.

'I'll tell you something, young man,' Derry said. 'If you are in any danger from the person who owns these knives, be very careful.' He considered his words. 'Normally knives such as these would be locked away. I find it disturbing that one was used used on Newmarket Heath.' on Newmarket Heath.'

'Could the police trace its owner?'

'Extremely unlikely,' he said. 'They didn't know where to begin, and I couldn't help them.'

'And the Armadillo's owner?'

He shook his head. 'Thousands will have been made. The Fury Armadillo does, I believe, have a serial number. It would identify when a particular knife was made and one might even trace it to its first owner. But from there it could be sold, stolen or given several times. I cannot envisage these knives you've seen being allowed into the light of day if they were traceable.'

Depressing, I thought.

I said, 'Professor, please show me your collection.'

'Certainly not.'

A pause.

I said, 'I'll tell you where I saw the Armadillo.'

'Go on, then.'

His old face was firm, his eyes unblinking. He promised nothing, but I needed more.

'A man I knew was murdered today,' I said. 'He was killed in a house in Newmarket with an ordinary kitchen knife. It is his mother's house. Last Sat.u.r.day, in the same house, his mother was badly slashed by a knife, but no weapons were found. She lived, and she's recovering in hospital. On the Heath, as I told you, we believe the star of our picture was an intended victim. The police are investigating all three of these things.'

He stared.

I went on. 'At first sight there seems to be no connection between today's murder and the attack on the Heath. I'm not sure, but I think that there may be.'

He frowned. 'Why do you think so?'

'A feeling. Too many knives all at once. And... well... do you remember Valentine Clark? He died of cancer a week ago today.'

Derry's stare grew ever more intense. When he didn't answer I said, 'It was Valentine's sister, Dorothea Pannier, who was slashed last Sat.u.r.day, in the house she shared with Valentine. The house was ransacked. Today her son Paul, Valentine's nephew, went to the house and was killed there. There is indeed someone very dangerous roaming around and if the police find him or her quickly... great.'

Unguessable thoughts occupied the professor's mind for whole long minutes. Finally he said, 'I became interested in knives when I was a boy. Someone gave me a Swiss Army knife with many blades. I treasured it.' He smiled briefly with small mouth movements. 'I was a lonely child. The knife made me feel more able to deal with the world. But there you are, that's how I think many people are drawn towards collecting, especially collecting weapons that one could use if one were... bolder, perhaps, or criminal. They are a crutch, a secret power.'

'I see,' I said, as he paused.

'Knives fascinated me,' Derry went on. 'They were my companions. I carried them everywhere. I had them strapped to my leg, or to my arm under my sleeve. I wore them on my belt. I felt warm with them, and more confident. Of course, it was adolescence... but as I grew older, I collected more, not less. I rationalised my feelings. I was a student, making a serious study, or so I thought. It went on for very many years, this sort of self-confidence. I became an acknowledged expert. I am, as you know, consulted consulted.'

'Yes.'

'Slowly, some years ago, my need for knives vanished. You may say that at about sixty-five I finally grew up. Even so, I've kept my knowledge of knives current, because consultancy fees, though infrequent, are welcome.'

'Mm.'

'I do still own a collection, as you realise, but I seldom look at it. I have left it to a museum in my will. If those young policemen had known of its existence, they had the power to take it away.'

'I can't believe it!'

With the long-suffering smile of a tutor for a dim student, he pulled open a drawer in his desk, fumbled around a little and produced a photo-copied sheet of paper, finely printed, which he handed to me.

I read the heading, PREVENTION OF CRIME ACT 1953 PREVENTION OF CRIME ACT 1953. OFFENSIVE WEAPONS OFFENSIVE WEAPONS.

'Take it and read it later,' he said. 'I give this to everyone who asks about knives. And now, young man, tell me where you saw the Armadillo.'

I paid my dues. I said, 'Someone stuck it into me. I saw it after it was pulled out.'

His mouth opened. I had really surprised him. He recovered a little and said, 'Was this a game game?'

'I think I was supposed to die. The knife hit a rib, and here I am.'

'Great G.o.d.' He thought. 'Then the police have the Armadillo also?'

'No,' I said. 'I've good reasons for not going to the police. So I'm trusting you, Professor.'

'Tell me the reasons.'

I explained about the moguls and their horror of jinxes. I said I wanted to complete the film, which I couldn't do with police intervention.

'You are as obsessed as anybody,' Derry judged.

'Very likely.'

He wanted to know where and how I had er, acquired acquired my first-hand knowledge of the knife in question, and I told him. I told him about the body protectors, and all about Robbie Gill's ministrations; all except the doctor's name. my first-hand knowledge of the knife in question, and I told him. I told him about the body protectors, and all about Robbie Gill's ministrations; all except the doctor's name.

When I stopped, I waited another long minute for his reaction. The old eyes watched me steadily.

He stood up. 'Come with me,' he said, and led the way through a brown door to an inner room, which proved to be his bedroom, a monastic-looking cell with a polished wood floor and a high old-fashioned iron bed with a white counterpane. There was a brown wooden wardrobe, a heavy chest of drawers and a single upright chair against plain white walls. The right ambience, I thought, for a mediaevalist.

He creaked down onto his knees by the bed as if about to say his prayers, but instead reached under the bedspread at floor level, and tugged.

A large wooden box on casters slowly rolled out, its dusty lid padlocked to the base. Roughly four feet long by three wide, it was at least a foot deep, and it looked formidably heavy.

The professor fumbled for a key ring which bore four keys only, and removed the padlock, opening the lid until it leaned back against the bed. Inside there was an expanse of green baize, and below that, when he removed it, row upon row of thin brown cardboard boxes, each bearing a neat white label with typewritten words identifying the contents. He looked them over, muttering that he hadn't inspected them for months, and picked out one of them, very much not at random.

'This,' he said, opening the narrow brown box, 'is a genuine commando knife, not a replica.'

The professor's commando knife was kept safe in bubble packing but, unwrapped, looked identical to the one sent to me as a warning, except that this one did have its sheath.

'I no longer,' he said unnecessarily, 'keep my knives on display. I packed them all away when my wife died, before I came here. She shared my interest, you see. She grew grew to be interested. I miss her.' to be interested. I miss her.'

'I'm sure you do.'

He closed the commando knife away and opened other treasures.

'These two knives from Persia, they have a curved blade, and handles and sheaths of engraved silver with lapis lazuli inserts. These are from j.a.pan... these from America, with carved bone handles in the shape of animal heads. All hand-made, of course. All magnificent specimens.'

All lethal, I thought.

'This beautiful knife is Russian, nineteenth century,' he said at one point. 'Closed, like this, it resembles, as you see, a Faberge egg, but in fact five separate blades open from it.' He pulled out the blades until they resembled a rosette of sharp leaves spreading out from the base of the egg-shaped grip, itself enamelled in blue and banded in fine gold.

'Er...' I said, 'your collection must be valuable. Why don't you sell it?'

'Young man, read the paper I gave you. It is illegal illegal to sell these things. One may now only give them to museums, not even to other individuals, and then only to museums that don't make a profit from exhibiting them.' to sell these things. One may now only give them to museums, not even to other individuals, and then only to museums that don't make a profit from exhibiting them.'

'It's amazing!'

'It stops law-abiding people in their tracks, but criminals take no notice. The world is as mediaeval as ever. Didn't you know?'

'I suspected it.'

His laugh cackled. 'Help me lift the top tray onto the bed. I'll show you some curiosities.'