It's August 1853, and there are pests aplenty on the docks of Melbourne, as the ship Madagascar prepares to sail for London. Built as a frigate, now working as a long-haul transport ship, it has proved itself on many a trip between England and India, transporting troops, spices, other goods.

Victoria is in the grip of a gold rush, and the Madagascar's captain, Fortescue Harris, has had to scrounge around for new crew after more than a dozen left to try their luck at the diggings.

On board, more than 100 passengers and 50 crew await the order to weigh anchor. Beneath their unsteady feet are bales of wool, rice, and an enviable ballast - almost three tonnes of gold.

Most passengers have paid £43 for a cabin, with a select few stumping up £84 for a first-class berth. Also sweating on the order to sail are two bushranger brothers, George and John Francis, who with their gang had three weeks earlier relieved a private gold escort of £10,000 worth of the shiny stuff. Freedom beckons at sea.

When the policemen make their way across the gangplank, it's not just the Francis boys who are feeling fidgety. Several on board, including some of the new hands, are dubious characters, and the game is up for someone.

In two days of police visits, the bushrangers are captured. Both would later inform on their gang - John getting a passage out of the colony in return; George ending his own life in custody. They may not have considered themselves lucky. But the Madagascar was heading for a watery grave. It sailed out of Port Phillip Heads on August 12, never to return.

Since 1853, it has been the subject of more speculation than almost any wreck. But there is a lot of water between Melbourne and Cape Horn, around which the Madagascar was headed, before turning north towards the Atlantic, and London.

Last month, amateur historian Gerald Crowley returned from a Pacific atoll where he believes he has found the ship.

Crowley does not conform to the image stored in your mind under the heading "treasure hunter". But if you ask him, he's not hunting treasure, just trying to save old stories.

The Oak Flats 48-year-old runs his pest control business a few days a week, helping fund his real passion, researching history.

"I'm just a history tragic," he said.

"Some people have no interest in history but for me it's part of my life. I get ... great satisfaction discovering things that have happened in the past that the general public don't know about - and it's always a good story to tell."

Crowley is happy to spend "four or five hours a night, seven days a week" researching his projects - which are often about missing treasure.

"Obsessed? Anyone who's passionate about history is obsessed," he said.

He says he's not in it for the booty - a claim supported by his modest lifestyle - but to discover lost knowledge. And like most historians, he fears that without someone filling in the missing bits, stories will be lost.

"We've got to be inclusive of all history. I think we're forgetting some of our colonial history, particularly our maritime history. There's a lot of things that may not be too salubrious but were actually part of our history ... the good and, unfortunately, the bad."

By "the bad", Crowley means piracy - the hijacking of the Madagascar, and the murder of almost all on board.

His theory is that out in the Pacific, the ship was hijacked, turned north, and sunk on a French Polynesian atoll. It is to this atoll, Anuanuraro, 1500 kilometres south-east of Tahiti, that Crowley travelled last month, with his French research partner, Albert Mata, to search for evidence.

Anuanuraro has an airstrip, crystal clear water, coconut palms and a sheltered lagoon, but you won't find James Packer and Miranda Kerr holidaying there.

It is a harsh and unforgiving climate; the air salty, the sea rough. Much of the shore is coral, not soft sand, and the central lagoon is busy with sharks.

Crowley's trip was tough - in rough seas, he opened up his head in a fall on the coral, and was taken off for treatment. A third member of their party, Mata's nephew, had to stay alone for days until he was retrieved by a navy helicopter.

But between this trip and another in 1997, Mata and Crowley have assembled a collection of artefacts that suggest the existence of a wreck. Crowley goes much further, pointing to a collection of factors that he says identify the Madagascar.

"There's a wreck. We're beyond doubt," he said.

"I can't prove it any more than actually physically showing you the pieces of it."

Retrieving a collection of pieces of the outer layer of the ship, he reaches for a kitchen knife and scrapes off layers of salt and dirt.

"See how it's yellow and shiny? That tells you something. If that was copper, it would be a copper colour. This is what we call Muntz metal."

Muntz metal (or yellow metal) was used to cover ships' hulls. It was cheaper and stronger than copper.

Crowley has nails made of copper and Muntz metal from the atoll, which fits with records showing the Madagascar was given a skin of Muntz metal early in 1853. He hasn't had it lab-tested yet but plans to.

A hand-blown bottle he found was probably pre-1860, because most bottles were made by machine after then.

An 1841 US expedition reported no sighting of a wreck, placing Crowley's artefacts between 1841 and 1860.

A sceptical journalist is trained to question evidence that is not conclusive, to interrogate assumptions and deductions, to look for a smoking gun - which for shipwreck hunters is the ship's bell, inscribed with its name. But in the absence of the bell, Crowley has to rely on the circumstantial.

"With all of these items, you've got to look holistically," he said. "In a perfect world I would have loved to have the bell with Madagascar written on it.

"I would say it's somewhere on the bottom of the sea, on the side of the atoll somewhere, well beyond the reach of my financial and diving capacities."

Mata also found in French archives a report from missionaries who were shipwrecked nearby. They made it to the atoll, and wrote about seeing a wreck already there.

Then there's the American.

Crowley and Mata met online and were researching the life of an American on the ship.

"We weren't looking for the Madagascar," Crowley said.

"We found the claims of an American who claimed [at this point Crowley lowers his voice] that he'd captured an Australian gold ship.

"We didn't know if it was all blarney, or some old fellow who had a bit of dementia ... but we started researching this man's life and we discovered a lot of the things he'd done in his life turns out to be true.

"Even in his 70s he was gunrunning to Cuba; in the 1870s he [was] supplying arms to the British Army off the coast of Africa to fight the Zulu.

"He was a bragger, he was a womaniser, but ... he gave clues. We needed to work through the clues, work through the lies ... and we finally found the pieces of the puzzle."

Being a hunt for missing gold, there's a point where Crowley gets cagey. Like when asked to name the American.

"There's some things I can say, and there's things I cannot say ... we won't because it's the subject of our book, and it's the subject of other parts of our research."

Nor will he say where the gold ended up, other than that it was taken off the ship, most likely to Tahiti, before the ship was set alight, with the passengers and crew dead, or about to die in the fire.

Our Oak Flats-Paris connection is not the only group investigating this mystery. One theory that Crowley believes is "quite plausible" is that the ship hit an iceberg on its way to the Cape of Good Hope.

Some say the Madagascar was wrecked in a swamp on North Stradbroke Island, north of Brisbane. A large bell was found there, and some think it may be the ship's bell. Crowley doesn't buy it.

"It's not up to me to run down anybody's theory," he said. "But the evidence just isn't there to support it."

He is convinced the Madagascar's fate was sealed at Anuanuraro.