OK, so, somebody drugged the wine the Doctor, the Prince, and the Prince’s two retainers drank. There’s only one other guy in the serial, and that’s Count Grendel, so he must be up to something.
And he really wants Romana for some reason.
That reason becomes more clear when we cut back to Grendel and find out what he’s up to. If Prince Reynart fails to show up for his coronation at the proper time, Grendel becomes king. And Romana? She’s an exact double for the Prince’s betrothed, Princess Strella. And yes, Grendel is holding her hostage too.
This Grendel guy is not a good guy.
Fortunately, the Doctor has a plan. Since there’s an android double for the Prince, the android can take the Prince’s place. The Doctor got it more or less working. And it would only have to be temporary.
He does need some help from K9, and he does warn the one swordsman not to draw his sword. That guy doesn’t listen until K9 hits him with his robo-canine snout beam.
So, can all this go wrong? Of course it can! Guards take Romana first to tend to Reynart and then later…somewhere else. The android Prince is damaged en route to the throne room, so it may not hold out for long. And while Grendel is surprised to see the Prince in the throne room, the android seems to mostly pull off what it has to do.
But then Strella steps forward to pledge her allegiance. Yes, the Doctor is initially surprised that she looks exactly like Romana, but why did he bash her head in with a staff when she bowed to the android Prince?
That kind of thing can get a person in a lot of trouble.