Once the taxi was clear of the airport I told the driver that I'd changed my mind. I wanted to go to Zoo Station. He looked at me and gave a knowing smile that was inimitably berlinerisch.

'Zoo Station,' he said. It was a squalid place, the Times Square of West Berlin. 'Alles klar.' In that district there was no shortage of people who would help a fugitive to hide from authority of any kind. The cab driver probably thought I was outsmarting the army cops, and he approved.

Yes, I thought, everything is clear. No sooner had I finished talking to him than the bloody D-G signalled to Berlin to have me arrested. It was artful to do it in Berlin. Here the army was king. Here I had no civil liberties that couldn't be overruled by regulations that dated from wartime. Here I could be locked away and forgotten. Yes, alles klar, Sir Henry. I am hooked.

Don't ask me what I hoped to achieve. I don't know what I was trying to do beyond gain time enough to collect my thoughts and see some way of extricating myself from this mess.

My mind worked frantically. I dismissed the idea of picking up the Smith & Wesson snub-nosed.38 and five hundred pounds' worth of mixed currency small denomination paper money that I used to keep in Lisl's safe but now kept in a twenty-four-hour safe-deposit box in the Ku-Damm. Neither ready cash nor flying lead would help me if the Department was after my blood. I dismissed too the Austrian passport that was sewn into the lining of a suitcase in a room in Marienfelde. I could become Austrian, if I raised my voice an octave and kept a tight grip on my nose. But what for; by Monday they would have good recent photos of me circulated, and being a phoney Austrian wouldn't help.

A taxi took Werner's box of china round to the hotel with a note for Ingrid Winter that I'd gone with Werner to the cinema. For anyone who knew us well, the idea of such an excursion was absurd. But Ingrid didn't know us very well, and it was the only excuse I could think of that would prevent her making inquiries about us for two or three hours.

Some of my actions were less well reasoned. As if driven by some demon from my over-active past, I took a second cab and asked for Checkpoint Charlie. It was almost night by now but my world was tilting towards the sun and it was not dark. My cab edged through the traffic as battalions of weary tourists wandered aimlessly around the neon and concrete charms of the Europa Centre and chewed popcorn and 'curry-wurst'.

'Checkpoint Charlie?' said the driver again just to be sure.

'Yes,' I said.

Once clear of the crowds we headed for the Canal. This quiet section of the city provides the shortest route to Checkpoint Charlie. No tourists walked the gently curving banks of the Landwehr Canal and yet there was more history in this short stretch than in the entire length of the Kurfursten Damm.

It was not always such a neglected backwater. The street names of yesterday tell their own story. Bendlerstrasse, from which the Wehrmacht marched to conquer Europe, is now named after Stauffenberg, architect of the failed anti-Nazi putsch. But is there some militaristic ambition burning deep inside the town planners who keep Bendler Bridge still Bendler Bridge?

Here on the canal bank is the building where Admiral Canaris, Hitler's chief of military intelligence, sat in his office plotting against his master. And into these murky waters the battered body of Rosa Luxemburg was thrown by the army's assassins.

Soon the dark tree-lined canal was left behind and the taxi was in Kreuzberg, speeding past Leuschner's Café and along Koch Strasse – Berlin 's Fleet Street – and to the Friedrichstrasse intersection that provides a view into the heart of East Berlin.

I paid off the cab and made a point of asking the American soldier on duty in the temporary hut, which has been positioned there for forty years, what time the checkpoint closed. It never closed, he told me; never! It was enough to make sure he remembered me passing through. If I was going to leave a trail that the MPs would follow, it would be better to make it wide and deep. The Department would not be fooled, but on past performance it would take a little time to get them into action. A Friday evening: Dicky Cruyer would have to be got back to his office from somewhere where the fishing and shooting was good and the telephoning demonstrably bad.

On the Western side of Checkpoint Charlie you'll find only a couple of well laid-back GIs lounging in a hut, but the Eastern side is crowded with gun-toting men in uniforms deliberately designed in the pattern of the old Prussian armies. I gave my passport to the surly DDR frontier guard who showed it to his senior officer who pushed it through the slot under the glass window. There it was photographed and put under the lights to find any secret marks that previous DDR frontier police might have put there. They gripped my passport with that proprietorial manner that all bureaucrats adopt towards identity papers. For men who man frontiers regard passports and manifests as communications to them from other bureaucrats in other lands. The bearers of such paper are no more than lowly messengers.

As a thinly disguised tax, all visitors are made to exchange Western money for DDR currency at an exorbitant rate. I paid. Guards came and went. Tourists formed a line. Buses and private cars crawled through and were examined underneath with the aid of large wheeled mirrors. A shiny new black Mercedes, flying the flag of some remote and impoverished African nation, was halted at the barrier behind a US army jeep that was demonstrating the victorious armies' right to patrol both sides of the city. The DDR guards did everything with a studied slowness. It all takes time: here everything takes time. And some of the victors have to be kept in their place.

East Berlin is virtually the only place to find a regime staunch and wholehearted in its application of the teachings of Karl Marx. Why not? Who could have doubted that the Germans, who had given such unquestioning faith and loyalty – not to mention countless million lives – to Kaiser Wilhelm and Adolf Hitler, would soldier on, long after Marxism had perished at its own hand and been relegated to the levelled Führerbunker of history.

The taller buildings around the shanty-town of huts that is Checkpoint Charlie give the feeling of being in an arena. So do the banners and the slogans. But the bellicose themes have gone. It is a time of retrenchment. The communist propaganda has abandoned the promises of outstripping the West in prosperity or converting it politically. Now the messages stress continuity and security and tell the proletariat to be grateful.

Emerging from Checkpoint Charlie you can see all the way to Friedrichstrasse station. There, a steel bridge crossing the street cuts a pattern in the indigo sky. Across the bridge go the trains that connect Paris with Warsaw and eventually Moscow, but the bridge itself is also the Friedrichstrasse station platform of the elevated S-Bahn, the commuter line that runs through both East and West Berlin.

The sight of the bridge gives the impression that the station is only a short walk, but the distance is deceptive and as I walked up Friedrichstrasse – past the blackened and pockmarked shells of bombed buildings that people said were owned by mysterious Swiss companies that even the DDR did not wish to offend – I remembered too late that it's worth getting a cab that short distance when one is in a hurry.

The S-Bahn station Friedrichstrasse provides another demonstration of the enormous workforce that the DDR devotes to manning the Wall. I went through its agonizingly slow passport control – there are even more checks on people leaving than on those entering – and eventually went through the tunnel and up to the platform.