The most exciting part of Doctor Who: Legend of the Sea Devils wasn't the special but the teaser trailer for the final special that revealed former companions from the classic show Tegan (Janet Fielding) and Ace (Sophie Aldred) would be showing up. The two of them formed the template for the female companions of the current show.
There's a reason this is a big deal: Tegan and Ace are the two real feminist companions of the show after Sarah Jane (Elizabeth Sladen), and even she spent way too much time being taken hostage and becoming a damsel-in-distress. This was the default sexism of male writers at the time. Even Louise Jameson, who played Leela, the warrior who was the Fourth Doctor's (Tom Baker) first companion after Sarah Jane left, had to fight to get her scripts changed. Neither Tegan nor Ace ever screamed at a monster coming after them.
Janet Fielding had ambitions when she was cast as Tegan to accompany the Fifth Doctor (Peter Davison) with Lyssa (Sarah Sutton) and Adric (Matthew Waterhouse). Describing herself as a "mouth on legs", she wanted to play Tegan as "Lucy van Pelt in space", a bolshy woman who took no crap from anyone and took charge when things got out of hand. Unfortunately, the scripts often failed her. Tegan was often reduced to hanging around complaining and asking what was going on for the Doctor to explain things. In real life, Fielding is very funny, snarky, and opinionated and it's a shame the writers never thought to write those aspects of her personality into Tegan. Her departure from the show felt sad and abrupt, with Tegan feeling it wasn't fun anymore, witnessing death and destruction wherever she went with the Doctor and walking away. An adult woman who didn't take any crap and had opinions, Tegan set the template for Donna Noble, where Catherine Tate had a chance to run as a mouthy, snarky, and funny companion who had no sexual or romantic interest at all in the Doctor but was his equal and best friend.
Sophie Aldred had a better time of it as Ace. Story editor Andrew Cartmel was determined to have a relatable, angry teenager who represented the kids of the 1980s – she was anti-racist, political, angry, and a bit of a delinquent in her love of destruction. She wore a bomber jacket with a Campaign for Nuclear Disarmament badge. She made bombs. She was the kind of kid who would show up on CND marches and the anti-poll tax demonstration of the 1980s. She was the most specific and relatable companion of the 1980s: an angry teen who hated her mother and burned down an old house, trying to channel her rage and aggression into doing something good. This made her the perfect companion to the increasingly manipulative Seventh Doctor (Sylvester McCoy) who became her mentor. She got to beat up a Dalek with a baseball bat! She had a complete arc during her two seasons on the show where the Doctor forced her to confront her issues with her mother and what drove her to burn down the old house in Perivale. She got to walk off into the sunset with the Doctor but didn't get a final season or ending because the show was canceled.
Tegan and Ace showing up in the Thirteenth Doctor's (Jodie Whittaker) final Doctor Who special should provide some closure for the characters and the actors playing them. And to fans. The special will probably be jam-packed with plot and other cameos, so we shouldn't get our hopes up too much. Hopefully, it won't be boring.