The last time John Harrison ventured into the jungle a member of his group died.

This time he brought his wife.

The Tumucumaque Hills on Brazil's northern frontier are one of the few remaining unexplored regions on earth. Back in 1950, a young French explorer set off into the deepest jungle of that region and was never seen again.

Inspired by that explorer's diary, John and Heather Harrison paddled their canoe into some of the remotest tributaries of the Amazon, with no TV cameras, sponsors or the slightest chance of being rescued if things went wrong. Lost, and threatened by malaria, snakes, jaguars, piranhas, aggressive wild pigs and flesh-burrowing insects, they slashed a precipitous path over the mountains.

This is travel at its rawest: the incredible story of the Harrisons' struggle to keep their deteriorating sanity and relationship intact in one of the most hostile and unforgiving places in the world.