The one where Romana almost becomes Queen of Tara...
I bet Prince Reynart is as disappointed as I am to see Romana back in his cell, after having helped her to escape in part 3. It makes the whole sub-plot of Romana's courageous escape on horseback mere padding, seeing as she ends up back at square one after all. She escaped in order to be captured. Oh, I hate that!
Grendel is never slow to come up with a new plan whenever his last one has been foiled, and now plans to marry Reynart to Romana/ Strella (delete as applicable), then kill Reynart and marry the grieving widow to become Queen's Consort. And then it'll be the Queen who will meet a nasty end, and Grendel will become rightful and lawful heir to the throne of Tara. However, we have to go through a scene in which Reynart rather intuitively tells Romana all this, before we get another scene in which Grendel confirms everything said in the last scene by telling the Archimandrite. Two scenes telling the viewer exactly the same information are not needed, and ends up just being padding (there's a good amount of padding in this story, and episode, too).