The two scientists relished life. They skied, went bushwalking and climbed mountains, often taking their three young daughters with them. Their cultural and intellectual pursuits were many - classical music, opera, literature, wine, arguments over dinner with their many friends. They donated 10 per cent of their annual income to political and environmental movements. Family events were spent thoroughly debating the topics of the day.

As their capacity declined, the conversation about ending their own lives became more serious and their rejection of what Peter called “religious do-gooders” became more fierce.

In April, Peter, an eminent meteorologist, was labouring. He sat down at his computer and typed a letter to his daughters, three highly educated women - two have PhDs and one is a concert violinist in Germany.

“It was also a way into their favourite topics; philosophy, ethics, politics, the law …,” says their youngest daughter, Kate. “The idea that their end-of-life decisions could be interfered with by people with the superstitions of medieval inquisitors astounded them, and alarmed them.”

“My head swims,” he wrote. “When I am reading, I can’t follow a difficult argument, so I give up, telling myself that it doesn’t matter, and I will read something else. I have just now been reading the history and politics arguments at the end of the latest Quarterly Essay and I am very disappointed that I can’t follow them.”

“My condition is getting worse bit by bit, slowly week by week. On top of all this, my eyesight and hearing are no good, my pulse is occasionally irregular. So how long can it go on? Weeks? Months? As you all know, I am not afraid of dying but I am dead scared of incompetence.”

Pat was also troubled by her old age. Arthritis was corroding her joints and she was getting dizzy, putting her at risk of another fall. She had swollen knees and hands, and was finding it increasingly difficult to get out of bed and out of chairs.

Following Peter’s letter, his daughters tried to keep him and Pat as content as possible. They visited more often. They tried to work out ways of helping. They attempted to cheer up the pair with fine whisky and wines. Surely they wouldn’t go when there was another bottle of duty-free Laphroaig in the pantry, Kate thought. But her parents had other plans.

Anny, their second daughter, asked if they could wait for one last Christmas. But they couldn’t. Or wouldn’t.

They set a date. Peter said it was time and Pat agreed. They would enter the “big sleep” together on October 27, the day after Pat’s 87th birthday.

Anny got on a plane. When she arrived in Melbourne on October 21, she was shocked at how frail her parents looked. She would often find her father slumped in his chair. Her mother was struggling to move in the purposeful way she used to. Anny showed them a DVD of concerts she had performed with the Munich Radio Orchestra. But she could see that her parents had changed. They were tired. Even a bit bored, she thought.

On their final night together, the family shared a last supper of sorts. The sisters prepared a plate of cheeses, avocado and smoked salmon to eat with wine. Peter and Pat pecked at it. They didn’t seem very interested in food. Anny picked up their grandmother’s violin and played for her parents. They went to bed around 10pm.

The next morning, Peter and Pat got up early. They showered, dressed and made their bed. Peter had breakfast, a fried egg and coffee. Pat did not eat. She wanted to keep her stomach empty for what was to come.

The family sat in their backyard in the soft morning sun, enjoying the native garden that had flourished around their Robin Boyd-style home. Peter had designed the house himself in the 1960s.

“They were more cheerful than I had seen them since I arrived,” Anny said.