Complex sentence: Argento finished the final film of his "Three Mothers" trilogy, "The Mother of Tears", which is set in Rome and centers on the titular "third mother", Mater Lacrimarum.
Split into simpler sentences: Argento finished the conclusion of his "Three Mothers" trilogy, "The Mother of Tears". The film is set in Rome and centers on the titular third mother, Mater Lacrimarum.