The life of Dr James Barry was and is by every measure so remarkable that at each turn of this quite gripping biography I found myself gasping in disbelief. A distinguished, celebrated military surgeon of both skill and modernising zeal, who fought for reforms to military hospitals in South Africa, the West Indies, St Helena and Canada, Barry died in 1865. Preparing his body for burial, the layer-out pulled back the sheet and found that the doctor was in fact a woman – who, moreover, had borne a child years before.

This part of the story is well known, and though the discovery caused much wonderment, it must have been less than a complete surprise to those who had known Barry. His odd and effeminate appearance was the cause of comment throughout his fifty-year career. ‘He was quite destitute of all the characters of manhood,’ wrote a colleague in Jamaica. Barry was tiny and beardless with a squeaky voice; his small, soft hands were often remarked on. He wore padded coats (in South Africa, local children called him ‘little Kapok maiden’) and two-inch heels. He was known to be obsessed with privacy when getting dressed or bathing. A nurse who came upon him half-naked was regarded henceforth with ‘implacable dislike’.

The really extraordinary nature of the story is not the subterfuge itself but Barry’s wild boldness and effrontery. What courage it must have taken to pull this adventure off – and what private loneliness it must also have entailed. Not only did Barry qualify and practise as a doctor at a time when women had entry to neither university nor the professions, but he actually joined the army and travelled to some of Britain’s remotest outposts, taking on the colonial authorities with fervour. He was there in the midst of cholera epidemics, tending the war-wounded, seeing first-hand (and working furiously to reform) the squalor and misery of prison hospitals, asylums and leper colonies. He was the first surgeon ever to perform a Caesarean section in which both mother and baby survived. In his early days studying in Edinburgh, his unmanly appearance was commented on, so he allowed the idea to spread that he was a teenage prodigy who had qualified in medicine aged twelve – and he got away with it. Barry was a fury, a force, a swaggering Regency dandy in a tricorn hat, wearing a sword almost as long as his five-foot height. He was also a teetotaller and a vegetarian. He fought a duel, was arrested twice and, in a scandal that rocked Cape Town society, was publicly accused of a homosexual affair with his friend and protector, the governor of the Cape.

Barry was born Margaret Ann Bulkley in Cork in 1789, the daughter of an impoverished butter inspector. It was hopeless debts that forced the fourteen-year-old Margaret and her mother, Mary Anne, to London to plead for help from Mary Anne’s brother, the celebrated, eccentric Royal Academician James Barry. It appears that during this time members of Barry’s radical, freethinking circle plotted to send Margaret to study medicine in Edinburgh in the guise of a young man. The idea perhaps was that she would then go to Venezuela with one of them, the revolutionary general Francisco de Miranda, to be part of a new nation emerging from Spanish rule. (Miranda died in 1816 so that was never to transpire, but James Barry took ‘Miranda’ as his second name.)

These details of Barry’s origins have been known for some time, but the excavations of Michael du Preez, a South African doctor, and Jeremy Dronfield in the papers of the elder James Barry have yielded startling new evidence about the period when Margaret became James. Among the correspondence of the elder Barry’s lawyer, Daniel Reardon, who annotated every letter with the name of its sender, they found a clinching letter from Dr James Barry marked ‘Miss M Bulkley’. They also discovered papers dealing with the finances of Margaret’s uncle Redmond, a drunken ne’er-do-well: du Preez and Dronfield make a convincing case for Redmond being the father of fourteen-year-old Margaret’s child, who was then passed off as her sister.

It is impossible to know whether the men who set in motion the metamorphosis of Margaret into James did so because they wanted to see if it could be done or whether they had seen something in a barely educated girl that was particularly unusual: someone who could make it work. It is hard not to think it was the latter. All his life James Barry had a talent for attracting the loyalty and encouragement of important patrons and friends. Reports sometimes mention his conversational charm, but this quality is difficult to convey on the page and it is easier to get a grasp of Barry’s enormous personality from his prickly contradictions. He was loved by the sick, with whom he was unusually tender, but he was also a tyrant who stood on his dignity and went out of his way to antagonise people who could make life difficult for him: quacks, officials, superior officers, bureaucrats and politicians. According to a contemporary, ‘his irritable and impatient temper brought him into constant collision with authority’. In old age, at Scutari, he tore a strip off Florence Nightingale, who thought him ‘the most hardened creature I ever met’.

The great pleasure of this book is its detail. It is one thing to re-create a life, but quite another to fill in the background as vividly as the authors have done, fleshing out the personalities of walk-on characters and giving colour and context to Barry’s world – or worlds. Wherever their subject goes, whether it is Margate or Mauritius, they make those places come alive with contemporary descriptions and reports. Their research is authoritative and prodigious, giving the reader glowing pictures of, for example, the rackety artistic circles of London in 1802, the horrors of a military hospital in wartime, travelling down a sheer South African gorge in a cart, visiting St Helena in the days of Napoleon, and being on a ship in which a smallpox infection breaks out. When you have all this to play with, the book’s occasional novelistic flourishes are surplus to requirements.

Barry’s remarkable life challenges a few received wisdoms about the past. It is true that Margaret Bulkley had to be James Barry to achieve all she did, but what is apparent from this book is the extent to which her true identity seems to have been curiously and protectively guarded by a surrounding society that questioned but did not pry. Barry was for the most part received by his world as the odd and brilliant maverick that he undoubtedly was.