When Japan invaded Hong Kong in 1941 a team working for Britain's wartime secret services led an escape party across 80 miles of occupied territory to safety. Colin McEwan was one of the team and his son-in-law Tim Luard returned to China to walk the same route.
Colin was a young man who had gone out from Scotland to teach in the Far East.
Colin McEwan's diary told of the escape from Japanese occupied Hong Kong
He found himself defending a colony that Britain had left almost defenceless.
Japan had already invaded much of China and now pressed home its attack on Hong Kong.
Later in life, my father-in-law seldom talked about the war.
But he did leave a diary and it tells of swimming under ships and blowing them up, and shooting fifth columnists in a street called Blood Alley. Things that are hard for the rest of us to imagine having to do.
And then came his escape, across the mountains of southern China. Fording rivers, eating tangerines from the tree - here was something we could imagine.
No sooner had she transcribed her father's diary than my wife, Alison, decided this was a journey we had to do ourselves.
I was soon poring over wartime maps and tracking down accounts left by other members of the escape party.
The group read a bit like a Hollywood cast list - including a one-legged Chinese admiral, a couple of very British cavalrymen from India, assorted spies and intelligence officers and a large and boisterous crew of Royal Navy sailors.
One-legged Admiral Chan Chak (right) was among the original escapers
We set out from Hong Kong on Christmas Day, as they had done.
We were just a gang of four, which gave us each a chance to adopt various roles with appropriate military hats - although my idea of being carried in a bamboo sedan chair like the admiral was given short shrift by my three female companions.
Having no motor torpedo boats to hand, we took the train across the border and then a bus along the Chinese coast.
"We landed on a lovely beach and moved off up a valley," wrote Colin.
In fact the beach has been reclaimed and turned into a concrete waterfront, lined with blocks of flats and garish hotels.
And just up behind the valley, the hamlet where they spent their first day, hiding from Japanese planes, is now buried under a reservoir.
We were aware that China had changed. And nowhere more so than around Hong Kong.
What was then a region of pirates' caves and smugglers' paths, paddy fields and wild plains, is now a hi-tech industrial zone of tunnels and flyovers, oil refineries and nuclear power stations.
Asking anyone where the "old path" was brought us baffled looks. "There is a new expressway just over there," they said. No one, these days, walks.
But we did - somehow. And the strange thing was how much, behind the surface, had survived - from ancestral halls with tiled roofs to village duck ponds guarded by barking dogs.
Officers and crew of the motor torpedo boat MTB 09 escaped Hong Kong
The diaries we had read in London burst into life. An old woman fortune-teller at a temple remembered how the foreigners had slept on the floor.
The fortress base of the local guerrillas who guided them is now a living museum - an ancient walled city in miniature.
Then there was the lychee orchard where they shivered one night on damp straw under the trees.
The farmer had said he could not ask them in or the Japanese would burn down his house.
There is still an orchard - even if it is now part of a luxury golf resort, aimed at today's weekend escapers from Hong Kong.
Tales of snakes
The high point in more ways than one was the mountain range, where one young naval officer had collapsed from exhaustion.
Despite attempts to put us off with tales of snakes and impenetrable undergrowth, we finally found a roguish beekeeper with a machete who agreed to escort us - for a fee.
He ended up as excited as we were, as we reopened the long-abandoned stone path up through the woods and over the ridge.
He had brought along the son of a communist guerrilla who had fought the Japanese here.
And he confirmed, as he studied my old army map, that these were indeed the same stones trodden by his and Alison's fathers.
The main escape party carried on all the way to Burma and back to Britain.
But Colin McEwan spent the rest of the war in the Pearl River Delta, helping others escape from Hong Kong.
He thought of going back later on to visit, but by then China was a closed country. Even a few years ago, when I was there as a journalist, doing the trip we have just done would have been impossible - at least without being shadowed by minders and police.
As it was, we met nothing but friendly curiosity. The 1941 party must have been a stranger sight still.
But they were welcomed with tea and rice as China's new allies in the fight against Japan.
The escape was an early example of genuine Sino-British co-operation after a century of deep mistrust.
The twin sons of the Chinese admiral and the families of other escapers are now planning a bigger re-enactment next year.
We will be there, with or without a bamboo sedan-chair.
From Our Own Correspondent was broadcast on Saturday, 7 February, 2009 at 1130 GMT on BBC Radio 4. Please check the programme schedules for World Service transmission times.