Two more Tom Baker ones.
An enslaved population, ruled over by evil, self-serving masters who have created a pseudo-religion complete with ritualistic sacrifice/execution. The Doctor gets involved with Leela causing the overthrow/destruction of the baddies and freeing the oppressed.
This was the storyline in general for both The Sun Makers and Underworld, though in different contexts. having them back to back felt a bit repetitive for me.