X. The Five Companions

From Big Finish News listing:

Eddie Robson's script is an exciting and rather tender reunion, in which the Fifth Doctor meets up with his distant past ? the schoolteacher who settled down, the space pilot who became a King, the security agent who died and lived again and the swinging Sixties secretary who has made her own way in the world.

16 out of 34 (47.1%) raters say this story requires a previous story.