Out 1, an immensely involving, addictive blend of film, literature and theater, has rightly been hailed as the Holy Grail of modern French cinema. Jacques Rivette — co-founder of the French New Wave with Jean-Luc Godard, François Truffaut, Éric Rohmer and Claude Chabrol — has always been that group’s most free-spirited, aesthetically radical member. This is very much on display in Out 1, his fourth feature film and magnum opus, in which a whimsical young man (Jean-Pierre Léaud) receives anonymous notes that put him on the trail of a mysterious group of people who might or might not be conspirators.