john vardy, wildlife photographer, riding the range in south africa's game reserve, on the trail of his she unlocked the secret world of the animal to me. >> reporter: first, a baby. it seems unfazed by humans. he can't believe he can get so close. what he and his trackers have is a rare front row seat over the course of almost two decades into the often solitary, stealthy, kill or be killed world of one of the most hauntingly beautiful animals on earth. strong, agile and fast, leopards are the smallest of the big cats. though they're big hunters, they, do, are hunted. only one of every two baby leopards survives to adulthood. when the mother's out chasing food, the cubs make easy prey for larger animals or even for male leopards who often kill their rival's offspring. and there are other dangers as well. when she and two of her cubs develop a deadly form of mange, vardy does something controversial to people in his provision. he intervenes. knowing there's a simple life-saving treatment, he darts mannana and the babies. it gives mannana 14 more years of life. and it's not an easy life.