"There is no slowing down now, only speeding up," says Dr Alan Rabinowitz during The Lost Land of the Tiger. "I don't have the time and the tigers don't have the time."
Over the last century, 98pc of the world's tiger population has been wiped out, first by big game hunters, and latterly by poachers, who kill these magnificent creatures and hack them to pieces.
And for what? Well, money, for one thing. The rarer tigers become, the more valuable they are to the poachers, who sell their bones and organs on the black market for traditional Chinese medicines.
In other words, so that some old man somewhere can get his withered hands on a tiger penis, which is said to have aphrodisiac qualities, and thereby revive another, even more withered part of his body.
Scientific studies have shown that the claims made for tiger penises are, if you'll pardon the expression, bollocks. But so far that's failed to prevent the carnage escalating.
There are only a few thousand tigers left in the wild. They could well disappear off the face of the planet within 10 years. Dr Rabinowitz could well disappear sooner.
He's dying from an incurable form of leukaemia. That's why he's led an expedition of scientists, wildlife experts and photographers to Bhutan in the Himalayas.
There are said to be tigers here, but no one knows if it's true, because tigers are notoriously elusive. And if it is true, no one has a clue how many of them there are. There could be a handful, or a there could be a thriving community. "This lost land of the tiger could be their last home," says Dr Rabinowitz.
It's easy to see why Bhutan is called the lost land. It's full of thick forest. If you want to penetrate it, the only way do so is by following animal trails, such as the elephants, who fell trees as they march on.
The team have brought a sniffer dog, a beautiful, chocolate-brown Labrador called Bruiser, with them. Bruiser is trained to sniff out tiger scent and tiger scat (that's droppings to you and me).
But Bruiser is feeling the heat and the humidity, and can only be worked for short periods before cooling down in a stream. Dr Rabinowitz's colleague Gordon Buchanan, on the other hand, is feeling the cold.
While the rest of the team are down below, looking for trails and placing motion-sensor video cameras on trees, he's high up in the Himalayas, where the temperatures are below freezing and the air so thin his lungs are burning.
Not even the mules carrying his equipment can make it beyond a certain altitude. At one point, he has to take off his freezing wet boots and cross a stream barefoot. Unbelievably, it's easier, safer and more comfortable to do it that way.
But it's not all about the tigers. While his colleagues are grabbing some sleep inside their tent, a Scottish insect expert called George McGavin creeps around outside in the dark. His job is to give the forest a "health check", to ascertain if it's capable of supporting tigers.
He's a character, is George, rooting through elephant dung and shouting "Bingo!" when he finds a dung beetle the size of a computer mouse. "You're beautiful!" he tells it.
But George cries when Dr Rabinowitz shows him a photograph of a tiger butchered for its skeleton, the rest of it dumped on the ground like a throw-rug. You'll cry too, because Lost Land of the Tiger is heartbreaking, though also gripping and thrilling and awe-inspiring.
Right at the end, the cameras capture a tiger. And then another. Everyone's ecstatic. The series continues tonight and concludes tomorrow. Follow the trail.
THE LOST LAND OF THE TIGER *****