He didn't look comforted. He said dully: "A quarter of the population of Europe. Did you say that?"

"At that time, twenty-five million people." My thoughts ran on aloud, just as they had at the Nurnberg Trial when I had spoken of Heinrich Zossen. "A heavy toll of human life, mein Hauptmann, Iagree. Even the Nazi plague of our own century wiped out only half that number in the death camps."

It didn't register. He was thinking of Argentina, and object number 73. I tied the ends for him: "Natural resistance to the pneumonic plague in South America is fairly low at present because there hasn't been an epidemic there for a long time, though it's endemic in Brazil, Peru and Ecuador. So I would say that if Dr. Rothstein's brother in the Argentine had opened that phial and tipped the contents from the balcony of a packed cinema, as instructed, the seventy thousand Germans and ex-Nazis in San Caterina would be dead within a week."

He said nothing for a full fifteen seconds.

"Herr Quiller… Why did he want to do this?"

"Because they killed his wife."

"But I do not understand. It is one of your little jokes, again."

"I hope you'll never understand. You're too young to understand. You must ask your elders. They know about these things. They killed twelve million people in five years. Half were Jews. And you can hear their reason for killing six million Judenfrei when you listen to them pleading their innocence at the courts. They say they killed them because they were ‘only Jews’. Nothing personal, you see. No hate, or thoughts of vengeance, or even fear. Just the Yellow Star, the selection-camp, and the gas-chamber. Difficult to understand. I understand Dr. Rothstein's reason better. He was committed to personal vengeance and it was measured solely by the depths of his love for one woman and by the desolation of her loss to him. And a thousand shall fall."

He got up and stood over me, a thin young man still trying to get to grips with the world he'd been born in.

"But the others! The plague wouldn't have stopped at any frontier. The whole of San Caterina – and then the whole of the Argentine -"

"And beyond, until they got the diagnosis correct and put the sulpha drugs to work. Rough justice is like that it takes the innocent as well. He knew that. He knew there are half a million of his own race in the Argentine but even that didn't stop him preparing that phial and writing this bequest to his brother. Dr. Rothstein meant to avenge his wife before he died, and if that wasn't possible he meant his death to bring it about."

Stettner looked down at me with his clear blue unimaginative eyes and I was impatient with him because I'd asked two of my questions about Solly's operational background and he didn't even catch on. Either that, or he didn't know anything more about Solly than I knew.

The day had gone badly for me and frustration was setting in. After two days' grinding work on the cipher I had produced nothing that would take me any nearer to Phoenix. This document could have nothing to do with what Solly had wanted to tell me. He wouldn't have any reason to tell me that his living obsession was to wipe out a South American town, because I couldn't be expected to champion the idea. Either his obsession had followed a normal course, pushing him across the edge of reason so that he was self-blinded to the risk of annihilating a whole continent, or he had made elaborate plans for his brother to organise an underground inoculation scheme to save the innocent before the plague was set on the march. It made no difference to me or to my mission. If Isaac Rothstein were a sane man he would have put the phial straight into an incinerator, realising his brother's state of mind.

Solly would never have told me of this. Then what had he been so desperate to tell me? There was no clue in the document, which was simply a detailed form of instruction to his brother: how the bacillus was to be disseminated, how to avoid infection during the act of dissemination, steps to be taken during the four-day incubation period, so forth.

There was of course an obvious parallel to be assumed, and it would have to be thought about later when I had left the aura of Captain Stettner's pathological horror of disease.

Because I knew that Solly had been doubling.

"I am grateful to you, Herr Quiller," Stettner was saying. "I shall of course take this decipherment straight to my superiors."

Before I went I asked him: "Did you find anything else in that laboratory, anything significant, anything you decided not to tell me about?"

He seemed surprised. "Nothing."

"I've done you a service, Herr Hauptmann, and you would be the first to reciprocrate. So I'll take your word that the canister was all you found."

"You have my word. Apart, of course, from the various papers we allowed you to see at the time. There was nothing else."

He wasn't lying. I wished he had been. It would have been something to bite on.

I left him and found the 230SL where I had parked it, half a kilometre from the Z Bureau. It was a model they'd never expect to find me driving, but once they'd got on to it they'd tag me at a distance because it was so distinctive, and distance-tagging was difficult to sense. They knew I might visit the Z Bureau at any time, so the car had been parked well clear. But I was expecting a tag to show up and there wasn't one. The half-kilometre was a dead clear run and I got into the car with a sense of foreboding. The rope they were giving me was getting longer, and I feared it.

Going over to the offensive was more difficult than I'd thought. Two days wasted on the Rothstein document, with still no clue to the way in.

There was only one feature of the day's work that eased my frustration: I now believed in Pol and in his briefing. The German General Staff did have – or might have – the means of triggering a non-nuclear war. Because of the parallel assumption.

Night was down and the streets shone with the aftermath of the sleet. There was a chance of getting the Mercedes into the Hotel Zentral lock-up without being recognised. If they still had a man posted in the bar at the corner he would be watching for the BMW.

I waited on the far side of the traffic-lights until a line of cars had built up, then followed the two who peeled off and took my street, keeping close behind them on the principle that one of three cars is less noticeable than if it travels alone. The windows of the bar were steamed-up but there was a black area low down in one corner and I turned my head away as I passed the place, swinging into the glass-roofed courtyard of the hotel with the riding-lights switched off.

The courtyard was oblong and the glass roof ran from the hotel building to the row of lock-ups. Observation could be kept on it only from the windows of the hotel itself and from a single house on the other side of the street, whose windows faced the open gates of the court. Three of these were lit and the fourth heavily-curtained. The lower windows of the hotel were of frosted glass and the five upper ones were all lit. I hadn't been seen putting the new image into the lock-up, though I might have been seen driving it into the court.

Findings: the 230SL was probably a good bet if I had to get away in a hurry.

Routine checks made on entering my room indicated no interference. They were keeping their distance, paying out the rope.

One hour's thought cleared up a lot of unanswered questions and posed some new ones. The Rothstein parallel assumption was given a thorough examination and still stood up. The frustration was eased a little and I even had the grace to send in a brief report to Control:

Correction to Signal 5. Container found at Rothstein lab. didn't carry microfilm but a phial charged with heavy culture of pneumonic plague bacillus and ciphered message to R's brother in Argentine detailing method of starting epidemic in San Caterina. Contact Captain Stettner Z Bureau if want details.