In a rapidly vanishing habitat on Brazil's Atlantic coast, the largest venomous snake in the Americas is on the verge of extinction. During months of drought, the Bushmaster has hidden from sight, and reptile hunter and scientist Mark O'Shea is in a race against the clock to capture the rare and deadly rainforest dweller and extract its venom. But it isn't known as The Ox-Killer for nothing.

The tiny South Atlantic outcrop of Queimada Grande is a Lost World, cut off from the rest of nature. There are no mammals, and to kill birds, the Golden Lancehead has evolved the most powerful venom of any snake in the Americas. Reptile hunter and scientist Mark O'Shea battles his way on to the impregnable island - but then has to face a deadly snake every ten paces.

The Patagonian Lancehead lives further south than any snake in the world. In a vast, windblown wilderness sloping down from the Andes Mountains, the venomous snake's behaviour is still a mystery to science. Reptile hunter and scientist Mark O'Shea heads into Patagonia to track it down, but he's never seen one before, and the Lancehead doesn't like being disturbed.

Mark O'Shea travels to Florida, to investigate a spectacular comeback by nature's great survivor. The crocodiles outlived the dinosaurs, but in the 1970s one species, the American Crocodile, went to the brink of extinction. Now the beast is back, and O'Shea wants to know the secret of its unique recovery - a quest that takes him on a night hunt through the eerie canals of a nuclear power plant.

The swamps of America's Deep South hide a secretive predator from the age of the dinosaurs. Even among the highly specialized killers of the reptile world, the Alligator Snapping Turtle is unique. Unsuspecting prey are deceived by a false worm in its gaping mouth, then ambushed in jaws that can splinter an alligator. But it's also a delicacy, and over-hunting has put the species in danger.

For Mark O'Shea, the Timber Rattlesnake is Nemesis. After a bite from a captive snake, he spent nine days in a hospital, close to death. But the Timber Rattlesnake itself is now in danger. That's where Mark aims to confront the species that nearly killed him, and help the scientists who are trying to save it. But the next bite could be fatal.