Inspired by the discovery of 185 long-forgotten cans of film, this documentary is a compelling account of the collapse of Les Diaboliques director Henri-Georges Clouzot's 1964 psychological thriller L'Enfer. The details of the location shoot are fascinating, especially as it's possible to see Italian star Serge Reggiani beginning to lose patience with his notoriously demanding director before eventually quitting the project. But it's the colour footage of the lighting and effects tests that Clouzot made with leading lady Romy Schneider that most seize the imagination. It suggests he was on the cusp of creating a masterpiece by exploiting avant-garde techniques to explore her character's tormented psyche as the jealousy of her husband (Reggiani) grows ever more pathological. With Jacques Gamblin and Bérénice Bejo enacting scenes from the original scenario (which was finally filmed by Claude Chabrol in 1994) and the likes of Costa-Gavras (a production assistant on the original movie) recalling the vicissitudes of the enterprise, this is perhaps the greatest "making of" documentary ever produced.

In 1964, Henri-Georges Clouzot's production of L'Enfer came to a halt. Despite huge expectations, major studio backing and an unlimited budget, after three weeks the production collapsed. This documentary presents Inferno's incredible expressionistic original rushes, screen tests, and on-location footage, whilst also reconstructing Clouzot's original vision, and shedding light on the ill-fated endeavor through interviews, dramatizations of unfilmed scenes, and Clouzot's own notes.