The Doctor is not impressed with Barbara, she's made the mistake of interfering, having tried to stop the sacrifice, she's made an enemy of Tlotoxl, he tries challenging Barbara's knowledge. Not done yet, Tlotoxl is contriving a battle between Ixta and Ian, she sets up a battle. The Doctor meets Ixta, whose father built the entrance to the tomb where the TARDIS lay, he explains he has a duel with Ian, and tries blackmailing the Doctor, a victory in the duel for the plans. Tlotoxl and Autloc overhear an indiscretion between The Doctor and Barbara, and imprison the Doctor. The Doctor can't warn Ian of the trick he's planning and the fight begins....
I think John Ringham was rather brilliant as Tlotoxl, being so used to his character 'Norman' in Just good friends, what a sharp contrast, he was a very good actor. Tlotoxl is a real villain. I've just watched and reviewed Colony in Space, they rather wasted him in that.
The acting is rather wonderful, it's faultless, not a single weak link. The script is just so good. I enjoyed the Doctor's romancing of Cameca in the garden. It's truly a lavish early adventure. 9/10