When James Blair, 15, realised his mother Ros was frantically signalling from the boat that had taken the family snorkelling in Thailand in December, one word came to mind: shark.
James, who was in the water about 100m away, swam as fast as he could to the boat.
What he saw when he got there will stay with him for ever. It had nothing to do with a shark attack.
A man wearing a lifejacket was being hauled aboard after James' cousin Murray Blair, 14, had swum into him and, realising he was face down and lifeless, towed him to the boat.
James, a lifesaver at the Floreat Surf Life Saving Club, had completed his bronze medallion just a week earlier.
He said yesterday he could remember "as clear as daylight" what his father, John, also on the boat, told him: "James, take a breath, you know what to do."
"That's when I knew I would have to resuscitate this man, or at least try," James said.
James' father told the boat driver to signal to a nearby boat from which the man had apparently come to follow as they sped to a nearby medical centre.
And James swung into action, directing family members to help as he and his father worked to revive the man with breaths and chest compressions.
Mrs Blair used bottled water to wash the man's mouth and provided water to James to wash his own mouth.
James' sister Jenna, 17, counted out the resuscitation cycle and Murray helped keep the man's body in the right position and clean his airways.
The boat trip took about 15 minutes but to James "it actually seemed like for ever".
As they pulled into Phi Phi Island bay, the man's lips went from pale blue to a richer colour, and then back to normal.
"At that point he was groaning, he was responsive, so he was alive and we knew that and I could feel a pulse," James said.
"He was conscious and breathing by himself. It was the best feeling I have had in my life."
At the beach they carried the victim into the medical centre, and a man from the victim's boat said he was a doctor and took over. Distraught relatives also arrived and James and his family stepped back and went to find a cool drink to process what had just happened.
When they returned the man had been taken to hospital.
The next day they tracked him down and when they called the hospital just before setting out to see him, they were told he had been discharged.
James said that in the immediate aftermath it almost seemed like a dream, but looking back he realised he had acted on instinct.
"Surf life saving trains you so well that it becomes part of your instinct," he said.
Floreat Surf Life Saving Club president Albert Iten said they were all proud of James and the rescue was a tribute to all those members who had helped equip him with the skills needed during a moment of crisis.
James' story will feature as part of a documentary series to mark a decade of Telstra's partnership with Surf Life Saving Australia.