Germans, Russians, Freemasons from several countries, Chinese, British, Americans and Eurasians among others mix genteelly in their final resting place. For those buried even up to the mid 20th century they probably mixed better in death than they did in life, with prejudice, lack of understanding, a sense of racial superiority and societal norms dictating that Hong Kong Chinese and Eurasians were second class.

Travellers giving early talks back in London would talk of the 'tricky' Chinese, says Lim, 'who were 'not to be trusted, you couldn't tell what they were thinking. They're all liars'. This carried on for decades, it's extraordinary.'

Several Norfolk pines rise majestically - testament to a time when their wood was used for the masts of Hong Kong's thriving shipping trade. Bird sound competes with the roar of the traffic coming in and out of the Aberdeen tunnel.

'I think it's a very peaceful place,' says Lim, who has spent hundreds of hours here, initially tracking every grave with fellow historian Ko Tim-keung as a voluntary project. 'But I found there were so many interesting stories of these people buried here that I wanted to find out more.'

So beginning at the gravesite, Lim then used diary accounts, newspaper reports from the day, books, the public records office, and the collection of the late Reverend Carl Smith, who tracked thousands of people in Hong Kong and wrote their details on cards. 'His collection was invaluable,' says Lim.

The result is Forgotten Souls: A Social History of the Hong Kong Cemetery published by Hong Kong University Press and one of the Royal Asiatic Society Hong Kong Studies series. It takes the stories of the people found by Lim among the 8,000 graves that still exist - 2,000 were demolished to make way for the Aberdeen tunnel - and breathes life into them, explaining the times in which they lived. The book encompasses the first decades of British rule in Hong Kong and provides a useful social history, a start on which Lim says others should build. 'I've barely scratched the surface, I'm hoping others will take up where I've left off,' she says.

Life in early colonial Hong Kong was grim. The average age of death for soldiers and police officers brought in from Britain was just 30. There are poignant small graves of children, gripped by disease after being given contaminated water.

'Henry Lovett here was murdered in 1853 by pirates,' says Lim. 'His ship was taken over by two of the passengers in the Chinese portion of the crew. The other English passengers jumped overboard and were never seen again. He was the ship's captain and was found with his guts hanging out and his poor, badly wounded bulldog standing by his side.'

Even the most adverse circumstances were no excuse to scrimp on decorum. 'Matilda Sharp, when in Vietnam on a shipping expedition with her husband, was waylaid by pirates after the ship was wrecked. She and her husband got on to a lifeboat, but beforehand she asked her amah to help her put on her crinoline and hooped skirt, as she said she had felt like a closed umbrella all day and looked awful.'

Then there were those who rebelled against the empress dowager at the start of the 20th century, and a man who Sun Yat-sen regarded as a proxy father. But what surprised Lim were the later graves such as the men who died in a plane crash just after the second world war with all the evidence on board to prosecute senior Japanese officers for war crimes. Then there were the young crew members who died in a shootout with a mainland gunboat in 1953.

There's also, somewhere, the grave of three mafoos and a horse, all hastily buried during the war - possibly after the Happy Valley stables were bombed. 'I don't know where that is,' says Lim, 'how big was the hole?'

Born Patricia DeFonblanque ('It's so much easier to spell Lim, isn't it?'), the grandmother of five comes from a line of French Huguenots, who converted to Catholicism. She was born in Pakistan to British army parents in 1934 - and then proceeded to have a charmed childhood. 'I was told I was sent back to Britain as a baby, but because the nanny had another baby as well as me to look after, I was neglected and I nearly died.

'I was in England during the war, but we then went to Berlin. I was in the Berlin Airlift. But the original plane I was supposed to be on crashed. I had chickenpox, and had to wait for another one.'

After Cambridge University, 'I had to get a job very quickly and the only one I could get was with MI5. I did telephone tapping, which was extremely boring. We listened out for Communists. It wasn't Islamic terrorists in those days. It was MPs communicating with Moscow.'

After becoming a teacher, Lim married Singaporean Po Chye and came to Hong Kong permanently 30 years ago. 'At the beginning my husband was very doubtful about [the project on the Happy Valley cemetery] because Chinese aren't very enamoured of cemeteries.

'But I don't find it creepy at all. Though there was one day I became so engrossed in what I was doing I forgot the time and when I got back to the gate, it was locked. So I had to climb out.'