Phung opened the door of the couple's black van, and turned to walk inside. But, before she could, a man jumped from a bush and stabbed her in the arm. Van came to his wife's aid, and fought off the man, but not before he was stabbed five times. As the grandfather lay bleeding in the driveway, the ambusher fled empty-handed into the darkness.

It looked as if the man had lain in wait to snatch the takings from the restaurant. Certainly, that's how the crime was portrayed the next day, including by police, and the couple's son, Vinh Le. But it was more complicated than that. And potentially far more lucrative.

Because Phung and Van did not just have the restaurant takings with them that night. According to police, they had about $40,000 - the funds from an informal Vietnamese loan system known as choi hui, which translates as "the game of borrowing".

The system, commonly known as hui, is remarkably popular in Vietnamese communities. It operates with a collection of families making regular contributions to a kitty, which any of them can borrow from at any time, if the loan is approved by others in the hui.

But repayments must be made by a set date, or else interest on the loan grows rapidly. In this way, members of the hui are also encouraged to delay borrowing until after others, as they will then be able to draw on the interest paid.

Most of the hui systems are small, like that which Van, 57, and Phung, 65, were involved in. But others grow to hold tens of millions of dollars. Either one person is appointed to chair the hui and hold the money, or the responsibility is rotated.

The attempted robbery in Maidstone on February 4 last year is one of the few crimes reported to police which may be linked to a hui. And even though it was reported, the investigation was problematic for detectives. The Vietnamese community was reticent to speak about who may have known Phung and Van may have had the hui that night.

The details of the allegations can now be revealed after Altona North Embona Taskforce detectives charged a 28-year-old man with attempted armed robbery, intentionally causing serious injury and intentionally causing injury. The St Albans man was charged on the May 8 and remanded to appear in the Melbourne Magistrates Court on August 1.

Hui systems, while not illegal, are considered particularly troublesome by police. Not only because those holding significant amounts of cash are more likely to become the victims of crime, as Van and Phung had been. But because those in debt to the hui are often forced to take desperate measures. It is not only the money owed which can be crushing; it can be the shame of being in debt to your friends and family.

A Swinburne University researcher, Roslyn Le, found that debts incurred through the hui system were forcing women into agreeing to become international drug couriers or to sit crop houses. In some cases, the hui had been used by gambling addicts to fund their habits, starting a dangerous spiral into crime, when they lost the money they had loaned.

The choi hui system started to help Vietnamese migrants quickly buy their own homes, start businesses, or help others migrate. It is similar to the rotating savings and credit associations, known as ROSCAs, which are common in developing countries.

Roslyn Le interviewed almost every Vietnamese women serving a Victorian prison sentence for a drug offence for her study Risky Business, which was published in 2014.

Several women said that being unable to pay loans from a hui was the reason they resorted to sitting a marijuana crop or imported drugs.

"Everyone plays hui. It's a way for us to save and borrow money," one prisoner, Veronica, said.

Another prisoner, Angela, described the system as like investment banking. "My mother's hui included people who were pretty well-known like shop owners; people with reputations," she said.

Some prisoners became involved in several hui at a time, compounding their huge debts, and others spoke about being the organisers of a hui, and having to reimburse members when other participants fled without paying what they owed.

The spiral which can befall someone saddled with debt related to a hui is perhaps best illustrated by Melbourne mother-of-three Thi Nguyen, who did not even owe money to the hui which wound up destroying her.

Thi was involved in a hui where one member fled with the money, and she in turn lost her restaurant and house. She became involved in a relationship with a man who helped her find a house, and then proposed she be involved in importing drugs from the US. Thi also enlisted a niece, who owed her money from another hui.

The drugs, hidden in a shipping container of foot spas, were intercepted by police in 2008. They seized almost 160 kilograms of drugs, including methamphetamine worth $50 million, cocaine worth as much as $32 million, and as much as $16 million worth of ecstasy.

Thi was sentenced to 12 years prison. It was her first conviction.

There has been some effort by police and politicians to warn the community against participating in a hui. Deputy Labor Party leader Anthony Albanese???, who is the member for Grayndler, an electorate in Sydney with a large Vietnamese population, told Federal Parliament in 2007 about the risks of the loan system.

He spoke about a police investigation into an administrator of a hui centred in Marrickville who allegedly defrauded the members of possibly tens of millions of dollars, funnelling the club's money offshore and into personal assets.

"While most hui take place between small groups of families, they can grow to enormous sizes involving tens of millions of dollars," he said.

"The potential for abuse and fraud, particularly by the chairman or administrator, is enormous. The chairman is responsible for large amounts of money, and that chairman is the only person aware of the amounts involved and often has sole control of the money.

"I am particularly concerned that it is vulnerable members of the Vietnamese community in my electorate who stand to lose, in many cases, their life savings. They have made representations to me and have asked that I make these issues public in order to warn other members of the community of the dangers which can take place."