Complex sentence: Early in the fourth season it is revealed that her goal is to free her beloved maker, the fallen angel Lucifer, from his imprisonment in Hell; the protagonists' attempts to thwart her plan is the main plot of the season.
Split into simpler sentences: Early in the fourth season it is revealed that her goal is to free her beloved maker, the fallen angel Lucifer, from his imprisonment in Hell. The protagonists' attempts to thwart her plan is the main plot of the season.