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.

3 out of 16 (18.8%) raters say this story requires a previous story.