Director Boorman alleges his mid-1980s' adventure is based on a true story. American construction chief Bill Markham (Boothe) is overseeing the building of a dam in the Amazon when his young son Tommy (Rodriguez) is kidnapped and hidden deep in the rainforest by a reclusive tribe, "the Invisible People," primitive natives who live in close harmony with nature, and can blend into what they consider paradise - lush jungle greenery.

Missing from home for a decade, the boy is initiated into manhood by a tribal rite-of-passage, and soon becomes part of the tribe. When his father finally finds him, the young white man, in a fine performance by the director's son Charley, has been fully adopted by the tribe, which deeply upsets his mother Jean (Meg Foster).

From the pivotal reunion, the movie shifts emphasis to mysticism, with Markham's hallucinatory experience as an 'animal spirit' (supposedly, everyone has one), and later to straight drama, as the tribe sets out to rescue their imprisoned women from slavery - in a guerrilla attack on the dam that represents a threat to the Invisible People's home and way of life.

Superbly photographed on location by Philippe Rousselot, "The Emerald Forest" combines documentary realism with marvellous fantasy (despite having almost no overt supernatural or paranormal elements), and a stirring, adventuresome narrative. Its episodic structure is weak, and sometimes the plot shifts are clumsy. But those are slight flaws, and can easily be overlooked in such an engrossing movie.