John Hopkins

On paper, the plan is simple.

Dave will swim down to the bottom of the chamber and place Dion's body into a specially designed silk body bag.

As he ascends, Don will be diving down to meet him at 220 meters, around 720 feet, where he will take possession of the body.

Don will then rise through the water and pass it to the next support diver and so on.

The relay process will continue until the body reaches the surface, thereby freeing up the divers who have been deepest and need to complete the longest decompression stops.

There are some clear rules.

If anything goes wrong, each person is to prioritize their own safety.

There are to be no heroics, and Dave and Don both publicly state that if they perish during the dive, they do not want to be recovered.

On the surface, the team will be coordinated by a dive marshal, Werner van Schijk, who set the women's world record for deepest scuba dive at the site just days before Dave discovered Dion's body.

If all goes to plan, the process should run like a well-oiled machine.

But despite all their preparations and precautions, when entering such a hostile environment, the slightest problem could have catastrophic ramifications.

Shortly after sunrise, everything is in place.

Just after 6am, Dave sinks out of sight beneath the water.

The focus then turns to timing the next diver's descents.

Don floats in the pool as the seconds slink by, staying calm and focusing on his breathing.

Twelve and a half minutes after Dave goes down, Don follows him.

He makes for a narrow opening at the bottom of the pool, a bottleneck which eventually opens up into the enormous chamber.

As Don descends, the slanting shafts of sunlight start to fade, and he enters a twilight zone.

The blackness closes in as he emerges into the upper section of the vast underwater cavern.

His torch illuminates the astonishingly clear water around him.