With only enough room in the air ambulance for one parent, Kirsten McMahon took the seat next to her son's body and braced for the long flight back to Melbourne.
The plane was tiny but her hopes, that doctors at home would be able to perform a life-affirming miracle, were immense.
But when they arrived on the 18th floor of the Royal Children's Hospital, she was met with condolences.
"Looking back on it … the medical teams understood the condition that Lachlan was in," Ms McMahon said.
Weeks earlier, Lachlan Cook boarded a flight to Vietnam, organised by the prestigious Kilvington Grammar School and World Challenge, an overseas adventure travel group.
Lachlan's father, Peter Cook, said the 16-year-old was thrilled about the trip.
"I can hear him now saying, 'This is me doing it on my own, going to a different country, different language, different food and working this out on my own'," Mr Cook said.
Lachlan had type 1 diabetes, but his parents were comfortable with letting him travel overseas.
After being diagnosed as a child, he'd learned how to manage his condition and measure his own blood-glucose levels.
"This was a soft landing for him," his mother, Ms McMahon, said.
"We were led to believe that there was 24-hour, seven-day-a-week medical assistance which at any time, if he needed it, then it would be called upon," she said.
On September 14, 2019, after getting the all-clear from his GP and paediatric endocrinologist, Lachlan and his schoolmates jetted off to Vietnam.
Mr Cook said his son was having a "hell of a great time".
"He rang me … going, 'Dad I want to buy a watch, is that okay?' That's the first and last time we heard of him on an entire trip," Mr Cook said.
"He wanted to buy a $10 watch from some market and 24 hours later, we're getting a phone call … saying that he's in hospital, in emergency, in a coma," he said.
"The world stopped."
A 'preventable' tragedy
How Lachlan Cook fell into a coma and was ultimately declared brain dead has been the subject of a bruising coronial inquest in Victoria, which is investigating whether the 16-year-old's death was preventable.
Both Kilvington Grammar and World Challenge have armed themselves with high-powered barristers who have been trying to temper how much blame their clients bear when coroner Audrey Jamieson eventually hands down her findings.
The coroner has already indicated that Lachlan's death could have been avoided.
"I will be making findings that there were a number of opportunities lost to provide appropriate oversight to Lachlan's type 1 diabetes in Vietnam and opportunities lost to provide him appropriate medical attention," she said earlier this year.
"I will be making a finding that his death was preventable," she said.
But the school and the adventure company are now facing a firefight on a different front.
Lachlan's family — his sister Isabel Cook, mum Kirsten McMahon and dad Peter Cook — have launched a lawsuit in the Supreme Court of Victoria, claiming that he died because Kilvington Grammar and World Challenge breached their duty of care to him.
The family is seeking unspecified damages.
"We may not have had to have gone down this track if we felt, actually, people have learned, they've taken accountability, but that was unfortunately not the case," Ms McMahon said.
"Peter and I, and Izzy, wouldn't have had to have been choosing a coffin for Lachlan, we wouldn't have had to have been providing eulogies at a funeral, we wouldn't have had to be facing every day without him if just one of them made a different choice," she said.
Their lawyer, Bree Knoester from Brave Legal, said children with all medical conditions should be able to go to camp.
"It's really important that schools and camps recognise that they need to take extra care of some kids, and they need to be prepared and they need to be trained and if they're not, kids can die, and the last image of your child should not be one of them in intensive care," Ms Knoester said.
"I could not be more convinced that both organisations breached their duty of care and that the death was preventable, and that the people charged with looking after Lachlan were untrained, underprepared and poorly managed," she said.
World Challenge's managing director, Peter Fletcher, declined to be interviewed for this story.
"Given the family has taken this action, it's now a matter for the courts so would be inappropriate for us to comment," Mr Fletcher said in an email.
A spokeswoman for Kilvington Grammar School also declined to comment.
"Out of respect for Lachie's family and the court process, it is not appropriate for the school to make any comment at this stage," she said.
"Our thoughts and prayers continue to be with Lachie's family and friends during this incredibly difficult time."
Four-hour 'communication breakdown'
After travelling close to 500 kilometres from the southern coastal town of Nha Trang to the ancient city of Hoi An, the Kilvington Grammar School group were ravenous.
They spent the evening exploring the lantern-lit laneways of the historic trading port, sampling street food and weaving their way through bustling markets.
It was only the following morning, on September 26, that Lachlan Cook started feeling unwell.
The inquest heard that Lachlan told Anna Walsh, the World Challenge expedition leader, he'd vomited twice and couldn't keep down any liquids.
With another student also unwell, Ms Walsh, who had first aid training, diagnosed both with gastroenteritis.
Lachlan continued to feel sick as the group made the four-hour bus ride from Hoi An to Hue, and was given small sips of Sprite, a sugary soft drink, because he was complaining of having no energy.
When asked, Lachlan told the expedition leader that his blood glucose levels were okay.
But later that night, as he continued to deteriorate, Ms Walsh phoned the World Challenge operations centre.
On the final day of the coronial inquest in June this year, Leading Senior Constable Dani Lord, who is assisting the coroner, said a crucial piece of information was left out during the conversation.
"World Challenge call-taker Stuart Thomas was not aware that Lachlan was a diabetic and it was not mentioned by Anna during the call, or when questioned about medication and symptoms," Leading Senior Constable Lord said.
Lachlan's condition prompted Matt Brinson, a Kilvington teacher, to call Ms McMahon, who urged him to check her son's blood-glucose levels every half an hour.
The expedition leader, Ms Walsh, then contacted the World Challenge operations again to ask if Lachlan's diabetes affected his treatment, but the inquest heard her message went unanswered.
The inquest heard that both World Challenge and Mr Thomas, the call taker, couldn't explain why there was then a lengthy delay.
"Critically when the message was read, and now aware of Lachlan's diabetes, Thomas was then unable to contact any adult on the trip for four hours to reassess Lachlan's condition," Leading Senior Constable Lord said.
"Had the communication breakdown not occurred, it is likely Thomas would have been able to escalate the medical support and this was a critical system failure."
Adults 'ill-equipped' to help Lachlan
In the early hours of the following morning Mr Brinson, from Kilvington, found Lachlan sitting at the end of his bed, breathing fast.
When the 16-year-old began slurring, he woke up Ms Walsh.
By this point, Lachlan was floppy and unresponsive.
Together they took a taxi to the Hue Hospital, where Mr Brinson used Google Translate to try and communicate with staff.
Lachlan was then moved to intensive care where his heart stopped, and he was urgently resuscitated for half an hour.
Forensic experts now know the 16-year-old was going through diabetic ketoacidosis, a serious complication of type 1 diabetes which happens when a patient's body cannot produce enough insulin.
The coronial inquest was told that none of the supervising adults on the trip had any specific training on how to manage diabetes, or "sufficient" knowledge of high blood glucose levels or diabetic ketoacidosis
It was told that another Kilvington teacher, who did have diabetes training, was not replaced when he pulled out of the trip.
The coroner also heard that Kilvington staff did not take a Diabetes Action Plan to Vietnam, even though it was taken on every school camp that Lachlan had ever attended.
"The constant theme through the evidence was that Kilvington staff relied on what they believed were the superior qualifications of Anna Walsh, and the medical backup of the World Challenge operation centre," Leading Senior Constable Lord said.
"The adults on the trip were ill-equipped to recognise and respond, in a timely manner, to Lachlan's deteriorating condition," she said.
Leading Senior Constable Lord told the coroner it was "unequivocal" that medical attention should have been sought sooner, and could have prevented Lachlan's deterioration.
"All the adults on the trip were reliant on Lachlan," Leading Senior Constable Lord said.
"As time passed during the day and into the evening, Lachlan's ability to self manage diminished," she said.
"When Lachlan did become unwell, it was apparent that no adult had a clear understanding … and therefore relied on Lachlan to guide them."
The inquest was told World Challenge has since conceded that knowledge of Lachlan's condition was "inadequate".
But Andrew Woods, who represented the family during the inquest, gave the coroner a more blistering assessment.
"On any view, leaving Lachlan's diabetes management entirely in Lachlan's own hands would be breathtakingly negligent," Mr Woods said.
"Lachlan was a child. He was in the care of adults. He was entrusted into Kilvington's and World Challenge's care," he said.
"Given the profound effects of ketoacidosis, [it] isn't known at what level Lachlan was cognitively functioning. He took the sugary drinks mistakenly offered to him throughout the day, the exact wrong thing to offer.
"In any event, he was a minor and so whatever his cognitive function, he cannot always be relied upon to make correct decisions at all times, that's why you have teachers in charge of students."
'There was no miracle'
Almost 24 hours after his heart stopped, Lachlan Cook was flown to Thailand where his loved ones rushed to be by his bedside.
For his parents and sister, whose last mental image of him was at Melbourne airport, and who wholly expected to next see him at the arrivals gate, it was as though the projector playing their lives had jammed.
"All of a sudden, we're at Bangkok International Hospital with our son with all these machines on him, and we're standing there and we're going, what the hell?" Mr Cook said.
"This was a perfectly normal boy, going on an adventure," he said.
In early October, Lachlan was flown to the Royal Children's Hospital where his family met with doctors, who declared him brain dead.
"There was no miracle that had been delivered," Ms McMahon said.
"I rang my parents and I said … 'You've got to come up here'," she said as she wept.
"How do you tell grandparents you've got to come up and say goodbye to your grandson?"
Together, they decided to switch off his life support.
"Thank God he had zero brain function because it made the decision for us," Mr Cook said.
Lachlan's heart, lungs and kidneys were donated to those in need, while his pancreas went to diabetes research.
'We were a family of four'
Two weeks after Lachlan died, Kilvington Grammar's then-principal, Jon Charlton, paid tribute to him in the school newsletter.
Days earlier, hundreds of mourners had gone to the 16-year-old's funeral to pay their respects, forming an honour guard as he was farewelled.
"Lachie will be profoundly missed by his classmates, teachers and the wider Kilvington community," Mr Charlton wrote.
"We extend our deepest sympathy to parents Kirsten and Peter, sister Izzy and his extended family."
Three years on, Lachlan's loss remains raw for many.
"I'm still seeing boys down the street now who just walk up and give me a hug," his father, Mr Cook, says.
But while Kilvington's commiserations still flow freely, the school has been immoveable on who it believes bore responsibility as Lachlan deteriorated.
On the final day of the coronial inquest Kilvington's lawyer, Mary Anne Hartley KC, said the school was kept in the dark by World Challenge and Lachlan's treating doctors.
"The school was led into a state of ignorance about many of the risks it was facing in relation to Lachlan," Ms Hartley said.
She told the coroner that Kilvington Grammar did not know the 16-year-old had difficulties with his diabetes, had not been sufficiently testing his blood glucose levels and had not received diabetes education for some time.
She said that Lachlan was not told by his paediatric endocrinologist that vomiting was a risk for a diabetic.
"If it had been informed accurately of the issues facing Lachlan … the school would have ensured active supervision of Lachlan, as the school had done previously," Ms Hartley said.
She also said that there was "no evidence" Lachlan's judgement was impaired earlier in the day when he was asked about his blood glucose levels.
Ms Hartley told the coroner that Kilvington Grammar believed World Challenge was responsible for all health emergencies, that it had 24-hour medical assistance available, and that its responsibility was to contact Lachlan's parents, which it did.
"The understanding of the school was that its teachers were accountable for the delivery of basic first aid, which is what they were trained to do," Ms Hartley said.
"It was also the school's understanding that the expedition leader would have overall responsibility for safety decisions, including the onset of problems from a pre-existing medical condition."
During the inquest, World Challenge accepted that its expedition leader, Ms Walsh, had a lack of diabetes knowledge.
But its lawyer, Fiona Ryan SC, urged the coroner to make the same findings against Kilvington's teachers.
"Kilvington has shirked from that criticism," Ms Ryan said.
"Rather the school's position appears to be that the knowledge and training of the teachers was adequate because the school relied totally on World Challenge.
"There's a clear disconnect between the school stance and the evidence that the school was in fact aware that first aid is a shared responsibility," she said.
She pointed to the school's historical involvement in previous trips and camps involving Lachlan, and said that Mr Brinson, who was on the trip, spoke to the teenager about his blood glucose levels.
"It is perplexing in light of these matters that the school's attitude is really to wash its hands."
The coroner is yet to hand down her findings but was told that "significant preventative changes" had already been made.
She was told that World Challenge had overhauled its medical management forms, instituted a phone volume policy, and now prompted call takers to check the medical history of students.
She also heard that specific diabetes training is now mandatory for all Kilvington Grammar staff, and that the school had modified its overseas trip policies.
But for Lachlan Cook's family, the changes come far too late.
"We were a family of four. We're now a family of three," Ms McMahon said.
"The impact he's had on us and on so many people, you can't take that way. But he won't turn 18, he won't turn 21, we won't be celebrating his university or marriage or grandchildren, there's none of that.
"We had 16 years."
