Welcome to the Badwater 135 Ultramarathon, the "world's toughest foot race", alternatively known as the "Race Through Hell".

Law, 36, will join 87 other diehard runners in the 36th edition of the race starting tomorrow in the appropriately named Death Valley in California. An invitational race, runners are hand-selected by a panel each year. Even after gaining entry and preparing their bodies for months on end, only two-thirds of competitors usually make it to the finish.

"I don't think there's a thing about this which is good for the body," says race co-ordinator Ben Jones in the 1999 documentary about the race, .

"Badwater is physically difficult because you have to tolerate the environment."

Starting at 86 metres below sea level, competitors run for 217 kilometres through one of the most forbidding deserts on earth while climbing over three mountain ranges for a total 3,962 metres of cumulative ascent.

Law will face near-certain dehydration, nausea, hallucinations and possible heat stroke. And that's just for starters. Then there are the more serious health issues such as kidney or liver failure. At times he will struggle to eat, making it difficult to summon the energy to walk.

"I want to know what it's like to stare death in the face," says Law.

His journey to Death Valley began six years ago, when he happened to watch a documentary about the gruelling endurance race. Even now, he can recall the anguished faces of the runners, convulsed in pain. "I remember thinking, 'Why on earth is this so difficult?' I wanted to find out for myself," says Law.

But Law has a secret weapon to get him through the challenge: Ida Lee, his wife.

The pair met eight years ago as members of a trail running team, the Cosmoboys. "We both love trail running and we have many common topics to talk about," says Lee. That they fell in love came as a surprise to both, because "we were quite focused on our training instead of thinking of our love affair", says Lee.

After accompanying Law to support him in a race in Australia, the relationship, and their unique brand of teamwork, was cemented.

Like Law, Lee has many kilometres under her belt, having completed the 160 kilometre Ultra-Trail du Mont Blanc through the French Alps in 2011 and the infamous Western States 100-Mile Endurance run in California last year.

She will be beside Law in a support vehicle every step of the way, monitoring his condition and offering encouragement. Four other runners will alternate shifts offering Law support during the race.

Though Lee holds high hopes for her husband, she's also concerned.

"Normally he's sensible, but if he's got a target that he wants very much, then he will try for it at any cost," she says. "When he puts on that race bib, he changes into another person; he becomes Chor-kin the runner. He says he will fight just like a soldier."

Law doesn't just run far, he runs fast. Together with teammate Thomas Lam, he created a new record during the Raleigh Tornado Challenge in Hong Kong last October, running the length of the 78 kilometre Wilson trail - and back - in 25 hours and 50 minutes. He was also part of the first mixed team over the line at the 2012 Oxfam Trailwalker.

But it's his compassion, not his tough veneer, which comes first to mind for 2012 Oxfam Trailwalker teammate Janet Ng. "He's definitely not one of those who wants to win at all costs," she says. "I've seen him giving his water to fellow competitors who didn't have enough."

Ng knows how important Badwater is to Law and believes Hong Kong has yet to see what the runner is truly capable of.

"He has incredible endurance levels - really off the charts," she says. "I have my fingers crossed that he will surprise everybody in Hong Kong with how well he is going to do."

Law also believes his Asian heritage will give him an advantage over the field of elite runners, which includes well-known American ultrarunner Dean Karnanzes, making his 11th attempt at the race. "Asians are built better for heat," Law says.

"We are skinnier and smaller, so physically I should be better prepared. I don't have as much fat in my muscles and I don't generate as much internal heat when I run."

Battling the sizzling temperatures while running during torturous Hong Kong summers has also provided good training.

Ultimately, Law says, running is a way he finds happiness.

"I like running for enjoyment and for the freedom it brings. It relaxes my mind and releases the pressure from work [as a surveyor]. I never think about gaining reward from running," he says. "I run for nothing. I run because I like running."

With hellish conditions predicted (temperatures of 57 degrees Celsius were recorded last week), it's difficult to understand how anyone can survive such a race, let alone do it with a smile.

Completing the mythical race - finding his limits and then exceeding them - is what Law says will give him his greatest happiness. Badwater is about finding out what he is truly made of.

While Law acknowledges that anything can happen on his journey, and that just finishing will be an achievement, he doesn't believe in limits and says he hopes for a top 10 finish.

"I think human beings have a lot of undiscovered potential. I believe the body has no limits. Even if you think you do, you will be able to break through them - if you have a strong desire and the mind to do so."

Badwater 135 Ultramarathon

Starts: Badwater, Death Valley, California, 85 metres below sea level

Ends: Mount Whitney, 2,500 metres above sea level

Distance: 217 kilometres (135 miles)

Course record (men): 22 hours, 51 minutes, 29 seconds by Valmir Nunes of Brazil

Course record (women): 26:16:12 by Jamie Donaldson of the USA