The 684th episode of Doctor Who airs on BBC1. Jean Marsh guest stars, and Nicholas Courtney makes his final original series appearance as Brigadier Lethbridge-Stewart. This story opens the 26th and final season of the original Doctor Who series. 
The 684th episode of Doctor Who airs on BBC1. Jean Marsh guest stars, and Nicholas Courtney makes his final original series appearance as Brigadier Lethbridge-Stewart. This story opens the 26th and final season of the original Doctor Who series.