The 1999 movie with the tagline "You can't prepare for where the truth will take you" is 8mm.
Joel Schumacher's dark crime thriller stars Nicolas Cage as Tom Welles, a private investigator hired to examine an apparently genuine film showing the murder of a young woman. What begins as a discreet authenticity check becomes an obsessive investigation into a violent underground film world.
Welles travels from his comfortable suburban life into increasingly dangerous territory, aided by Max California, played by Joaquin Phoenix. The case forces him to confront exploitation, criminality, and the psychological cost of pursuing disturbing truths. James Gandolfini plays Eddie Poole, one of the film's threatening figures.
Written by Andrew Kevin Walker, 8mm was released in February 1999. The title refers to the 8 mm film format used for the reel at the center of the mystery. It is sometimes confused with other late-1990s Nicolas Cage thrillers, but this tagline and investigation specifically belong to 8mm.