Werner Herzog has for years examined risk-taking individuals. He has also emerged as a green prophet of our time, fascinated by the beauty of the world, even as it appears to be vanishing.

These two themes come together in The White Diamond, a film about the building and operation by a British engineer of a miniature helium balloon capable of hugging the treetops of the rain forest.

Its pilot and passenger can peer down into the complexity of life beneath. But this is Werner Herzog - and there is a plot and extensive back-story.