More than $100 million has vanished in a financial scandal at the heart of the federal government's disability housing program.

One enterprise lured in more than 500 Australians with the promise of glittering high returns and social good, only to be exposed as one of the country's most audacious investment scams.

Investors were told their money would help tackle the disability housing crisis while earning government backed, fixed returns. Instead, $78 million is alleged to have disappeared into a web of failed projects, luxury cars, gambling sprees and offshore ventures.

This week on Four Corners, reporter Jessica Longbottom reveals the cracks in the governance of Australia's disability housing market and exposes systemic regulatory failure.

The government's Specialist Disability Accommodation program, part of the NDIS, was meant to transform lives, but it was handed to a poorly regulated private sector.

Four Corners investigates how the program, marketed as an ethical investment, has turned into a feeding ground for property sharks and led to streets of vacant homes across the country.

The program asks: is this once in a generation opportunity at risk of collapse amid fraud, waste and shattered trust?

The race is on to find the minerals we need to enable the world's transition to clean energy, and vast reserves of those minerals lie untouched at the bottom of the Pacific.

But, while mining them could fuel our green future, scientists warn it risks catastrophic damage to our oceans.

Enter Australian entrepreneur Gerard Barron, the founder and CEO of The Metals Company.

He wants to extract potato-sized balls called polymetallic nodules from the seabed and believes they could be worth trillions of dollars.

His project has gained political momentum after US President Donald Trump signed an executive order supporting seabed mining, even in international waters.

The United Nations affiliated agency responsible for regulating the exploitation of the world's deep-sea resources says mining under US permits would be unlawful and undermines global cooperation.

With no clear rules in place, and the stakes higher than ever, the future of deep-sea mining is now a global flashpoint.

Reporter Mark Willacy travels from Jamaica to Tonga to Washington D.C. to investigate the battle over who controls the ocean, who profits from its resources, and what the world could stand to lose.

Race to the Bottom is a stunning film that reveals a growing divide between political ambition, corporate interests and environmental responsibility.

Race to the Bottom, reported by Mark Willacy and produced by Mary Fallon, goes to air on Monday 8 September at 8.30pm on ABC TV and ABC iview.