​The words, coming from the chairwoman of the board's ethics committee, were intended to be reassuring: "I'm really glad to have you in that role. I really am," she said.

Dr Kirstin Ferguson was speaking to David* who for more than two years had been working to stamp out alleged corruption and misconduct within his company. David was suffering stress and anxiety because he feared - with good reason - that his boss was cutting him loose.

But two weeks later Ferguson's reassurances meant nothing. David was given three months' notice and told to go immediately on "garden leave".

The company was Thiess, part of Leighton group, which has been implicated in among the most serious foreign bribery and corruption cases in recent Australian history. David's boss was then Thiess managing director Bruce Munro, who later left the company under a cloud.

As for the ethics committee chairwoman, Dr Ferguson: she is still there, and still in the top integrity role at the firm, since renamed CIMIC. She has since scored one of the most high-profile jobs in Australia - she was appointed by the Coalition government as a director of the ABC board, where she is a member of its audit and risk committee, the body in charge of overseeing ethical behaviour.

David is working again, busy remaking his career. But it remains to be seen if he'll ever rise again to the heights of corporate success he once enjoyed.

He declined to speak to Fairfax Media, but his full story can now be told for the first time through documents held by Thiess and CIMIC, and leaked by a source close to both firms.

His story is a stark example of the peril in speaking truth to power in corporate Australia. It's shocking not just because of the individual impact on David, but because those involved in his alleged mistreatment have never been held to account. They include Dr Ferguson.

In the United States, someone who came forward with information about corporate malfeasance might be paid millions of dollars. In Australia, speaking out is a shortcut to dismissal, despair and unemployment.

And so far in this country, whistleblowers cannot even console themselves that the bad guys will be held to account for the deeds exposed, given the difficulty often facing police or the corporate regulator in investigating, prosecuting and punishing large companies.

Project Orange

David's faith in his company was first shaken in November 2011. As one of Thiess' more senior figures, David came across a document, signed by his boss Bruce Munro more than three years earlier, as part of the company's 2008 tender for a $5.5 billion mining concession in India.

It quickly became clear that the deal might have had at its heart a corrupt arrangement. Documents and key emails suggested that Thiess' business partner in India would be paying $12 million to powerful Indian government officials - an apparently illegal payment under Australian law.

Munro had been careful with whom he shared details of Thiess' partnership with this Indian businessman. In court documents linked to the whistleblower's case, it's alleged that Munro explained to the whistleblower that the sticklers for good process inside the firm would have "never let me sign it [a deal with the Indian partner]". Alarmed at what he had seen, David escalated the emails and Leighton senior management ordered an external investigation. It was codenamed "Project Orange."

Then the bullying began.

"If I go down, I am taking you down with me. I am not joking," Munro allegedly told David.

When the Project Orange investigation was completed, it suggested Leighton may need to inform the Australian Stock Exchange of a foreign bribery matter. Munro had breached the company's code of ethics and internal policies, the report found. However, there was not yet enough evidence for criminal charges.

After that, precisely nothing happened. The market was not informed. Munro kept his job.

Project Mango

In 2012, Leighton first informed the market it was under investigation for paying bribes for unrelated contracts in Iraq to build an oil pipeline.

But strangely - and potentially illegally - Leighton later stayed quiet about Thiess' Indian activities. It released an ASX announcement on October 3, 2013, emphasising in bold "we are not aware of any new allegations or instances of corruption [outside of Iraq]".

This appears to have been false. Many months earlier, Leighton had been handed the Project Orange report about the highly suspect Indian dealings.

Inside Leighton, some were concerned the company might have a deep ethical problem. So a new confidential internal review, Project Mango, was ordered into whether Leighton might be exposed to corruption issues elsewhere. It turned up about 100 payments made by Thiess employees in Indonesia to the country's government, military and policing officials.

Not everyone appreciated the revelation.

"This company is f---ed," Munro objected. "All this investigation and looking up its own arse. You can quote me on that," he allegedly said to David, who was involved in the new investigation.

Munro was concerned that risk and compliance activities were cramping the style of those whose job it was to win contracts in difficult markets.

"I want you to ... have a look and tell them [senior management] that there is nothing to see here ... We are tying people up in paperwork. Our processes have gone too far".

'Naively noble'

Meanwhile, at the corporate level, things were changing. In March 2014, as Project Mango was underway, Leighton was taken over by a Spanish group and eventually renamed CIMIC. But if anyone hoped the change of management would lead to a more open culture, those hopes were quickly snuffed.

The senior executives who had commissioned Project Mango were sacked and the new bosses wanted it shut down. The story about the payments to Indonesian soldiers was reported, via a leak, in Fairfax Media. But instead of performing a mea culpa, an internal witch hunt for the leakers began.

Those working on Project Mango were pressured to file a report "that confirmed that there were no corruption issues and that the matter was concluded".

Even then, David did not see himself as a whistleblower. He was just doing his job. That job, though, was getting harder. He felt increasingly harassed and pressured, caught between the need to do the right thing, and the orders of his bosses to shut it down. He was told the problem was to be taken back "internally within Thiess", according to the new chief financial officer.

Still Munro was not happy. He accused David of being "naively noble". Munro warned him that he was going to be stripped of a key part of his role.

David was having trouble sleeping. Often anxious, he developed a skin rash that his doctor attributed to the mounting stress.

Tidying up

By May 2014, Leighton was tidying up. At the AGM that year, the termination payments of the sacked CEO and CFO would be decided. It was time to rule a line under past scandals.

A week before that crucial meeting, the board called David to the Sydney offices of the company's lawyers, to address the corruption allegations. The board decided to punish Munro (who declined to comment when contacted this week by Fairfax). But they did not sack him; they simply docked his bonus.

Munro was angry. He told colleagues he believed Project Orange had been designed simply to attack him, and he blamed David.

David felt increasingly isolated. Over time, his health deteriorated.

Munro, on the other hand, was promoted. He became the managing director of Leighton's mining business, amalgamated under the Thiess banner. In the restructure, he would have the power to appoint people to the new positions within his team.

Court documents allege that, during one meeting, he strongly implied to David that he did not trust him. After two years of reporting wrongdoing to the right places, David's job was seriously under threat.

A breath of fresh air

The tidy-up brought one ray of hope. In July 2014, Dr Kirstin Ferguson, a former flight lieutenant in the air force, an expert in safety, a lawyer, a PhD in corporate governance and a professional company director, became the head of CIMIC's ethics committee.

Two weeks after her appointment, David rang her. He wanted to meet for coffee. He asked if she knew about what had happened in India, if she was aware of Project Orange.

"If I were in your position, I would want to know this," he said of the "biggest ethical issue the company has and would be the biggest ever in Australia."

"I do. I really do," she replied, adding reassuringly: "I'm really glad that we have you in that role."

David also warned Ferguson (who declined to respond to detailed questions from Fairfax Media) that his job was in peril for speaking out.

Ferguson said she'd get back to him.

David's lawyers later argued his conversation with Ferguson should have been a "protected disclosure" under Australia's flawed whistleblower regime.

But a fortnight later, David received a call from the "manager of people" at CIMIC. He was told he "hasn't made it in the restructure". He'd lost his job, and was sent immediately on three months gardening leave.

Then came the coda.

Two days later, Dr Ferguson sent David a text. To a person humiliated, isolated and sacked for trying to report wrongdoing in front of him, the message rubbed salt into his wounds.

"Hi - just wanted to let you know I have been following up on your call and will be sure to call you when done," Dr Ferguson wrote. It might take another couple of weeks, she said.

"I'm somewhat surprised," he replied "to hear from you in the circumstances of the termination of my employment".

David requested urgent help. Silence ensued.

"Kirstin, when can I expect to hear from you?"

He never did.

* Not his real name