The story of Max Price and Brenda Hean
It was September 1972, three months before Labor's Gough Whitlam won power, and environmental activists - for the first time in Australia's history - had political muscle.
One was greenie Brenda Hean, a conservative Tasmanian matriarch who was causing enormous waves in her home state and on the mainland by helping lead an aggressive national campaign to save the pristine Lake Pedder.
On September 8, 1972, Hean, 55, hopped aboard a two-seater World War II Tiger Moth, being flown by experienced pilot Max Price. Leaving from Hobart, they were bound for Canberra to try to win support from federal politicians to stop the flooding of Lake Pedder by Tasmania's Hydro Electricity Commission.
One of their intentions was to skywrite Save Lake Pedder over the national capital.
The plane never made it, and the bodies and wreckage were never located.
Thirty-two years later, Greens Senator Bob Brown - declaring the deaths possibly the first political murders in Australian history - wants a full public inquiry into the disappearance.
A request at the time for a royal commission or independent inquiry was refused by the police, the state Labor government and the federal Liberal government, led by Billy McMahon. The case was never declared closed by Tasmanian police and no coronial inquest was held
On the ABC-TV program Rewind tonight, the original investigator of the case, former assistant police commissioner Ernie Roffe, denies there was any cover-up.
Why then, Senator Brown asks, did it take Tasmanian authorities 18 years to respond to repeated requests for the case files?
At Rewind's request, Tasmanian police recently reviewed the case notes and declared that the case had been properly investigated. But Senator Brown believes the only way to put the mystery to rest is to hold a full inquiry.
Aviation safety investigators found no clues to the disappearance, although they deduced the plane may have crashed between the Tasmanian mainland and Flinders Island.
Environmentalists, however, continue to maintain that the plane was sabotaged and the pair's presumed deaths were therefore murder.
A few days before Hean and Price took off for Canberra, the activist told friends she had received a telephone death threat.
The anonymous caller told her to drop the campaign or suffer the consequences, ending with the chilling words: "I hope you can swim."
Compounding the suspicions of Hean's friends, a break-in at the hangar where the Tiger Moth was stored was revealed after the plane went missing.
Police discovered a door of the hangar had been broken into but nothing had been stolen. Only a few papers had been disturbed. Members of the Save Lake Pedder campaign believed the break-in was before the flight and that the purpose was to tamper with the plane.
Former activists have told Rewind they believe people in the then state government or the Hydro Electricity Commission may have known more about what happened than they revealed.
"There are many people who feel that the conjunction of events which saw that plane crash and disappear has a whole cloud of sinister questions hanging over it," said Senator Brown. "There should be the judicial inquiry that wasn't allowed in 1972 in the cauldron of the Lake Pedder furor, which was then spilling out into a national controversy."
When he started research for the program, producer Peter George didn't accept the conspiracy theory about the deaths. Now, he's open to thinking otherwise.
"The activists involved are older, wiser and more conservative, yet even with the cooling-off period of 32 years they remain absolutely convinced that there is more to be discovered," he said.
Lake Pedder was flooded in March 1973 and the campaign was recognized as the first great national environmental struggle.