John Hopkins

It's 4 a.m.

on Saturday, January the 8th, 2005.

In South Africa, the skies above the Kalahari Desert are still black, the landscape cloaked in the blanket of night.

Inside a small lodge on Mount Carmel Game Farm, some 300 miles southwest of Johannesburg, an alarm breaks the silence of a dark room shared by two men, 48-year-old Don Shirley and 50-year-old Dave Shaw.

The two friends stretch and yawn, then set about the business of showering and getting ready for the day ahead.

Their actions are ordinary, offering no hint of the vast undertaking that lies ahead of them.

After a light breakfast, the two men climb into Don's pickup truck and pull away from the lodge.

In the pre-dawn darkness, they drive east through the desert, their vehicle bouncing along the rough dirt track.

Their destination is Bushman's Hole, one of the largest and most dangerous freshwater caves on the planet.

It has a known depth of around 280 meters, over 900 feet, but could go even deeper.

But Bushman's Hole is legendary in the diving community for more than just its depth.

In December 1994, tragedy struck.

A 20-year-old diver named Dion Dreher died in the cave after losing consciousness around 50 or 60 meters down.

His body was never found until nearly 10 years later when Dave Shaw stumbled upon him, frozen in time on the cave floor.

And today, after months of planning, Dave, Don, and a team of other divers will try to recover Dion's body and return him to his family.

It's an ambitious project, but if anyone's up to the task, it's these men.

Although, incredibly, Dave only learned to dive in 1999, he has achieved meteoric success, rising in a handful of years from a novice to one of the world's most skilled and audacious divers.

Don, meanwhile, has been at this for decades and is a respected, well-known instructor with a wealth of experience.

Raised in Egham, near London, Don's passion started at the age of 10, after a visit to Wookie Hole in southern England, an impressive cave system featuring a number of underwater chambers and tunnels.

Young Don was entranced.