Complex sentence: Leela's parents, convinced that Leela did not show up because she is ashamed of them slink back to the sewers, just a moment before Leela rushes out onto the street to greet them.
Split into simpler sentences: Leela's parents are convinced that Leela did not meet them because she is ashamed of them. They slink back to the sewers, just a moment before Leela rushes out onto the street to greet them.