Trudie Adams disappeared without a trace. Then her mother received a haunting phone call.

Trudie Adams was 18 when she went to a party at the Newport Surf Lifesaving Club, asking her mum, Connie, to wait up for her.

It was 1978 and Trudie had grown up on Sydney’s Northern Beaches – known by many as the ‘insular peninsula’ because it felt like an entirely different world to the rest of Sydney.

On a Saturday night in June, Trudie left the Newport dance party early, and planned to hitchhike home. Just after midnight, her ex-boyfriend, Steven Norris, saw her get into a car on Barrenjoey Road. It was the last time anyone would ever see Trudie Adams.

When she didn’t return home, her family reported her missing.

But five days after her daughter’s disappearance, Trudie’s mother Connie received a haunting phone call. A male voice said, “Trudie is dead.”

“You will find her about half way up Mona Vale Road. It was an accident.”

An identical phone call was made to Mona Vale police.

In response, police searched an area of 400 square kilometres, much of which was dense bushland, along Mona Vale Road. No trace of Trudie was found.

The mystery of Trudie Adams’ disappearance is now the focus of the ABC’s true crime podcast Unravel. The series examines how the case has remained unsolved for 40 years, and the police corruption that might have played a part.

In the months after Trudie’s disappearance, 14 young women came forward to report sexual assaults and attempted abductions in the Mona Vale area. The women’s accounts took place over a period beginning in 1971, and involved being blindfolded, handcuffed, and held at gunpoint.

Over the decades, the investigation into what happened to Trudie Adams went in a number of different directions, but at a 2011 inquest, the coroner stated she had probably died of “homicide” or “misadventure followed by a cover-up”.

At the inquest, a former NSW police detective named two men he ‘strongly believed’ were responsible for Adams’ murder. One of those men is currently in prison serving an 18-year sentence for drug-related crimes, and the other died in 2010.

For Trudie’s friends and family, however, it would mean everything to learn what happened to the social, independent 18-year-old who had her whole life ahead of her.

Trudie’s mother Connie died 10 years after her daughter’s disappearance.

At the 2011 inquest, Trudie’s 81-year-old father said his wife had died of a “broken heart”.

Listen to Unravel here.