The night before he disappeared, Dennis Lee Thian Poh called his wife in Kuala Lumpur. They chatted about the bitter cold in Nepal's Annapurna range and he said that dinner in his small lodge had consisted, yet again, of vegetable fried rice.

Lee, 47, had been hiking for six days in Nepal's most visited trekking zone, the Annapurna Conservation Area.

The next morning, Lee told the eight other trekkers in his group that he was going to walk ahead of them, catch up with their porters and then meet up at lunchtime. As of April 15, Lee has been missing for 11 days.

"He has always wanted, for the longest time, to go to Nepal," says his wife, Jennifer Peters-Lee, who flew to Nepal to follow the search at a town in the Annapurna area.

Dennis had had second thoughts about the trek, Jennifer says. He was uncertain about leaving her to juggle her job and his two teenage daughters from his earlier marriage, one of whom has autism. But Jennifer, who's not a hiker, had assured him she and the girls would be fine.

The area where Dennis disappeared is mostly above 11,800 feet elevation. It's between the tiny hamlets of Khopra Danda and Bayali in the center of the Annapurna Circuit, with an achingly beautiful panorama of mountains, rising nearly 26,000 feet above sea level.

The region is also one of Nepal's most dangerous for trekkers. The mountains collect moisture from the area, resulting in frequent rain, hail and snow. Once a trekker heads higher into the mountains, like Dennis' group did, wide walking paths and stone steps are replaced by narrow, slippery and unstable paths, often on the edge of vertical precipices.

Last season, a sign was posted on the track to Bayali warning trekkers not to walk it solo. It's unclear whether the group guide warned Dennis, and no one knows whether he saw the sign.

"People always underestimate the mountains," says Jit Bahadur Masrangi Magar, director of operations at SAR Dogs Nepal, the group that's spearheading the search for Dennis with four of its dogs. "The mountains are not your friends. So many people believe they can do it alone."

Eight of the world's 10 highest mountains are in Nepal, and tourism — especially mountain adventure and trekking — is a backbone of the country's economy.

About 800,000 visitors come each year from all over the world and in increasing numbers from China, Southeast Asia and Israel. The Annapurna Circuit, a favorite trekking destination, was once just traversable on foot. Now it's crisscrossed with rough and, at times, terrifying dirt roads, passable only in four-wheel drive vehicles. Adventurous tourists increasingly aim for areas that are more isolated and more pristine, such as the path to Bayali.

But when trekkers go missing, the odds of finding them are low. And you don't have to be hiking on Everest to get lost.

"It is surprisingly easy to disappear in the mountains here, especially if you are trekking alone," says a diplomat in Kathmandu.

The U.S. State Department warns visitors not to trek alone and urges everyone to register with the embassy in Kathmandu, where the consular section has pictures of missing American trekkers posted on the walls of its visitor area. Some trekkers' remains are not found for years.

SAR Dogs Nepal, the country's main dog search and rescue organization, functions entirely on donations. In 2014, the agency rescued five foreigners and about 200 Nepalis.

And it's not just the rugged terrain and weather that hinder rescue operations. Linguistic and cultural barriers, weak government infrastructure and disorganized communication channels slow down searches.

Dennis' trekking guide immediately started searching for him when he disappeared. But the company waited 48 hours to alert local authorities, the dog teams and Dennis' family. Dennis managed to place a call that never went through. Rescuers traced the call's location. But they made a mistake, at first, which further delayed the identification of the general area where he disappeared.

The head of the SAR Dogs Nepal team searching for Dennis is a 29-year-old fine arts major from the village of Lamjung in the nearby hills. Karna Dura grew up around dogs and the search and rescue world. He knows intimately the odds and complexities of survival.

In 2013, Dura and SAR Dogs Nepal found the body of a German trekker missing for 22 days after they believe he fell down a gorge as he left the trail to get a better angle to take pictures. He had managed to survive until a few days before SAR Dogs Nepal found him. The trekker had filmed his last few days and a message to his family on his camera.

In 1991, an Australian man disappeared in northern Nepal, surviving 43 days before being rescued. Unlike Dennis, both these men were trekking solo without a group and not on a set route.

If a trekker is fully fit and does not have a head injury, trackers with SAR Dogs believe it's possible to survive three to four weeks in the mountains. Dennis, an avid and fit hiker, has a black belt in taekwondo. In his day-pack, he had a warm winter jacket, about 2 pints of water, a knife, a compass and some muesli. Now the weather is Dura's biggest enemy.

Working with a 10-man team, three air-scenting dogs and one dog that tracks a person, Dura and his team have identified four spots where Dennis was. One spot is a boulder, marking Dennis' last location on the main trail halfway to Bayali. The team is using Dennis' boots, sleeping bag and clothes that the porters were carrying to give the dogs his scent.

But large boulders below this site, combined with heavy fog and rain, make it impossible for the team to see down the ravine. Though they have been joined by 60 local villagers and six policemen, poor visibility has blocked helicopter assistance. Rappelling is the only way down the gorge, and the army is coming Thursday with professional rappellers.

Snow and hail for the past few days have kept nighttime temperatures below freezing. The trail is a slippery mud morass.

"This is very stressful," Dura says in a phone call from Bayali, which at over 13,000 feet elevation is cloaked in snow. "I pray he is all right."

Dennis' wife, Jennifer, struggles to hold onto hope. But she also feels her world is crumbling. She has made fliers with Dennis' picture, with the offer of a reward, to be distributed to local Nepali villagers. "I am so desperate," she says. "I have written a letter to the prime minister of Malaysia asking him for help."

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