Having begun his filmmaking career with the groundbreaking Citizen Kane, Orson Welles conjured up, in the last decade of his life, another hugely innovative masterpiece. The term ‘documentary’ doesn’t do justice to this marvellously erudite and mischievously witty mix of archive footage, home-movie, magic tricks, rumination, fiction and… well, yes, documentary. On one level, it examines the ‘evidence’ (mainly found footage, though Welles, already playing our urbane host, manages to be on show there too) regarding a notorious case of questionable authorship: Clifford Irving’s possibly bogus biography of his friend Elmyr de Hory, himself a forger responsible for countless paintings – but which? – in the world’s top collections. More than that, however, it’s also a bracing meditation on art from Chartres to Picasso, a wry confession of Welles’ own history of hoaxes, and a meticulously mounted collage of the countless fertile ideas percolating in his own brilliantly inventive head. As an improbably honest summary of Welles’ extraordinary achievements, it’s resonant and revealing; as a profoundly philosophical but engagingly playful commentary on human creativity, it’s absolutely spellbinding.