This suggested that I had been under close observation and might still be. If I were, some face which was familiar to me on my own street or station ought to turn up again on the underground or on my usual routes to the London Library, to the museum, to lunch. When in London I had become very much a creature of habit.

But I could not see a sign that I was followed. That was not surprising if my regular routine had already been checked. For example, it is not necessary for me to disturb an animal by following it about. After a period of patient observation I know what it is likely to be doing and where it is likely to be found at any given time.

I did not change my habits. It was not worth either the trouble or the reproving of myself for undue nervousness. I was still only admitting that it was possible, just faintly possible, that I had been the intended victim of that parcel.

Then there was a curious incident. Not another attempt on me. Nothing but a message, and a very clear one. I received a pamphlet published by some politico-religious society with revolting — and true —photographs of German concentration camps. There was a small cross in one corner of a picture of Buchenwald. It covered the officer’s mess.

Language is a clumsy way of communication. It takes me thirty-five words to convey the meaning of that cross. Something of this sort:

“You do not appear to be worried. That is a pity. I wish you to be worried. I wish it so much that I do not care if this message sends you to the police.”

The sender could not of course know what I had or had not told the police, but there was no sign that I was being guarded. I must have appeared to him very unimaginative.

All the same it was safe to assume that he would keep clear of my house and street for the next few weeks. The danger, if there really was any, would be outside. I took the precaution of moving about by unusual routes at unexpected times and avoiding the edge of underground platforms.

Meanwhile I wrote to an old friend in the Ministry of Justice at Vienna. We had lost sight of each other since 1943, but the bond was close. We were both Austrians with a tradition behind us which made us loathe Hitler and every one of his crazed fanatics. I came directly under his orders in the private war which we carried on under instructions from London. The English are too inclined to think of Germans and Austrians as one people. They forget — if they ever knew — that thousands of us were executed for sabotage.

His reply was immensely cordial. He looked back on that period with enjoyment. Well, perhaps we did enjoy it —for the first year. Death at the hands of the Gestapo had never been, in a sense, more than a day away and we gambled with it. We avoided the thought that if we were caught death would certainly be several months away and that when it came we should be without nails, teeth, sleep or sanity.

He seemed surprised at my question. He thought the murders would have been reported in British papers. I don’t think they ever were. The only foreign murders which interest the British are French.

“There have been no known cases of revenge,” he wrote, “except upon the former staff of Buchenwald. A certain Gustav Sporn, Major, was shot dead outside his home two days after his release from prison. The assassin left no clue to his identity, and nobody greatly cared. Sporn seems to have been an unspeakable brute, and German opinion (though of course, being what they are, they would never admit it) was that the Allies should have hanged him instead of letting him off with a ten-year sentence.

“A month later Captain Walter Dickfuss came out. He was decoyed to a ruined factory where, according to the medical evidence, he was kept alive with great ingenuity for three days. The medicolegal authorities were so shocked by the appearance of the corpse that investigation was and is most thorough.

“Obviously the criminal is some poor devil who survived the horrors of Buchenwald. But all possible suspects have been checked. Nothing fits.

“The third to go was a fellow called Hans Weber against whom there seems to be nothing at all except that he served in the Gestapo and was a guard at Buchenwald — if one can call that nothing. German police believe that Dickfuss implicated him by some confession, possibly false, during torture.

“His was an interesting case, for he was killed in spite of —one might almost say because of — police protection. He was stabbed in a crowd, recovered from a very nasty wound and was then well watched day and night.

“The watch began to slack off after a couple of months, as it always does, but the executioner was more patient. All the police know of him — and they are certain of it — is that he must have plenty of money and unlimited time at his disposal.

“He pretended to be a cop, frightened Weber out of his life, rushed him round a corner for safety, gave him a drink from his hip-flask. And that was that. The hipflask is conjecture. The rest is the evidence of Weber’s wife. She says that the man was above average height. Otherwise her description of him is worthless. She heard the quick conversation at the front door of the flat, but only caught a glimpse of the man’s back as he and Weber rushed out. He must have watched the flat until he was sure of the hour when she put the children to bed.

“We learned in a hard school not to ask unnecessary questions, old friend, but I am bursting with curiosity. If you are on the trail of the murderer — or shall we call him an executioner? — take it up with Scotland Yard. They will presumably have details of all three cases from Interpol.”

There was only one man in whom I felt able to confide. Even him I had avoided for years. I called him up at his farm near Buckingham and asked him to meet me urgently in London at some spot where we could not possibly be seen together. My plan was vaguely forming — clear enough to foresee that there should be no observable connection between us. He told me that he had the use of a friend’s flat and made an appointment for the following day.

Singleton Court was a huge, red-brick block of small flats, built in the middle nineteen-thirties — a regular warren of holes for respectable rabbits without young. As I wandered along the heavily carpeted passages looking for Number 66, I wished we had had something of the sort in central Vienna. Not even a continental concierge could have reported accurately the movements, political tastes and professions behind such an architect’s fever dream of white-painted, closed front doors. If I had been followed by my enemy —and I reckoned he had experience of how and how not to follow—he could never discover on whom I had called.

The door of 66 opened at once when I rang the bell. At the sight of Ian Parrow I felt a curious mixture of affection and resentment. He carried me back eleven years into a life which had become mercifully unreal to the zoologist. And yet that strained, thin face which smiled in the doorway — a face which used to give the impression of lank, black hair and office-white skin as marked as a waiter’s uniform —had meant to me such personal safety as I could have, and safety, still more important, for my honor and reputation. The thin mouth which had been too tense for a soldier had relaxed.

And now I must confess my secret. Even today I hate to put it on paper. Yet I suppose every one of us, whatever the nationality, who fought without a uniform or, worse still, in the enemy’s, must have memories which defile him and from which he shudders away. Perhaps the aristocratic tradition of my family made it harder for me than most. But the two thousand years of Christianity behind a proud and self-respecting boiler-maker are just as powerful.

My father used to say that the claim of the von Dennims to any Empire of Germans was rather better than that of the Hapsburgs. So it is, if you conveniently ignore —as he did —that our direct descent from the House of Hohenstaufen began with a daughter. However, by 1922, when I was ten, orphaned, and collecting cheese rinds from other people’s garbage cans, the point was of minor importance.