Complex sentence: The movie was written by Robert L. Joseph, Ida Lupino and Collier Young, with uncredited assistance from "Out of the Past" screenwriter Daniel Mainwaring, who was blacklisted at the time.
Split into simpler sentences: The movie was written by Robert L. Joseph, Ida Lupino and Collier Young. Uncredited writing help was provided by "Out of the Past" screenwriter Daniel Mainwaring, who was blacklisted at the time.