The Grammar Of Happiness follows the story of Daniel Everett among the extraordinary 'nonconvertible' Amazonian Pirah tribe, a group of indigenous hunter- gatherers whose culture and outlook on life has taken the world of linguistics by storm. As a young ambitious missionary three decades ago, Dan, a red-bearded towering American, decamped to the Amazon rain forest to save indigenous souls. His assignment was to translate the book of Mark into the tongue of the Pirah, a people whose puzzling speech seemed unrelated to any other on Earth. What he learned during his time with the Pirah led him to question the very foundations of his own deep beliefs. As a 'born again' atheist, Dan divorced his devout Christian wife and became estranged from his children. Having lost faith and family, his new life is dominated by the desire to leave behind his legacy. Everett's most controversial claim is that the Pirah language lacks 'recursion' - the ability to build an infinite number of sentences.

• Documentary