Even so, Sheriff of Wan Chai reveals Mann’s intellect, if not his charm. His mother, Margaret, wrote the Merlin series and came from an illustrious line of church people and academics in colonial India. The author was educated at the traditionally churchy Monkton Combe School and won a place at Oxford, where he became captain of boats at Exeter College. However, Mann seems reluctant to write about his personal relationships, and as a result is hard to place, know or like. His parents have cameo roles with his siblings, and his stepfather merits only an untitled portrait in a restaurant.

The author also seems to have observed rather than lived his Oxford years, as he says too little of his rowing teammates, classmates, tutors or any intellectual influences there. Mann spots writers J. R. R. Tolkien and W. H. Auden around town, but doesn’t talk to them. He says he meets Tony Blair, but fails to record anything the future British premier said. Manns’ lovers are also reduced to timeline bit parts, such as the “tearful” Julia; the “attractive” Lilian; and even his “long-suffering” wife Zoe – until she offers him wise investment advice.

The author also fluffs his best lines. In the vice squad, Mann bravely chases a suspect down 17 flights of stairs, but doesn’t describe the search operation’s planning, teamwork, or how he felt during the chase. Some readers might also wonder whether Mann slammed the suspect’s head against a wall in 1970s style, shouting the Cantonese version of “you’re nicked”, but the author makes no further effort at audience engagement.

Mann also pulls a gun on 50 suspects and seizes bundles of cash in a raid on an illegal casino, but the anecdote takes up just two paragraphs. A more imaginative writer might have opened a chapter with the stories of two failed swoops to reflect the frustrations of unreliable intelligence and the dangers of armed undercover policing – and then closed it with the sweetness of a good tip-off, Mann’s coup and any celebrations with colleagues.

The author’s descriptions of Hong Kong’s vice scene also seem twee. He records a police station report room as a “veritable cathouse of pouting girls” but shields readers from the shock and maybe the trousers-down, bright-lights humour of a brothel raid. He reveals the traditional profit split of girlie drinks, but does not dwell on the prostitutes he interviewed, or the dangers and rewards of the “oldest profession” in late 1970s Hong Kong. Instead, the author catalogues the history of triads and flits to detailed recollections of Lantau until page 60, when he leaves the force.

Mann’s readers might wish he hadn’t. He joins the colonial government’s administrative service section and recalls his experiences in drab vignettes of forgettable municipal jobs that largely lack the humour or the local charm of Austin Coates’ Myself a Mandarin. He writes of his “lively discussions” on democracy with governor Chris Patten, but doesn’t say much. Too many of his more junior colleagues are anonymous, as he pads his chapters with more diversions, from Puerto Galera to Ghana and Peru.

The author develops a knowledge of local trees, however. He reminds Hongkongers when they bloom and discourses on banyans. He catalogues the handover 15 years too late and leaves the civil service in 2001, writing that he was “too much of a free spirit to feel comfortable under the new civil-service regime”. He then dabbles in business, teaches, and spouts more Hong Kong history, from Sars to Occupy Central. Mann embraces Buddhism, cites its similarities with Christianity, and then reveals a day’s prayer and meditation practice – in the third person.

Sheriff of Wan Chai leaves Mann writing his memoirs in the teahouses of Xinhui, Gangdong, where locals praise the “amazing” quality of his Cantonese. However, this book’s readers might wish Mann was as engaging in English.