The Third Doctor and Liz

This period of the show lasted only one season, with Barry Letts realizing (correctly) that if the Doctor had an intellectual equal as his companion, there wouldn’t be much for Liz to do, hurting her development. In Big Finish terms, this section had been pretty short because Caroline John passed away in 2012, before Big Finish had committed to Third Doctor stories. However, with the advent of Tim Treloar as the Doctor, and Daisy Ashford taking over her mother’s role as Liz, this section is starting to fill out now.