Complex sentence: Dix knows Laurel didn't see Mildred leave, so when he gets home, he checks up on Laurel and finds out that she is an aspiring actress, with only a few low-budget films to her credit.
Split into simpler sentences: Dix knows Laurel lied about seeing Mildred leave, so when he gets home, he checks up on her. He finds out that she is an aspiring actress, with only a few low-budget films to her credit.