This is shaping up to be a bad year for 70's era Doctor Who companions. The BBC is reporting that Mary Tamm, who played Romana I,
had died from cancer.
When I was young and watching Doctor Who meant endless repeats of Tom Baker's era on PBS, I always looked forward to The Key to Time season rolling around again. At the time, I'd have put it down to the sheer novelty of a story arc that lasted and entire season (!), but when I watched the season on DVD again recently, I realized how much of it was due to Mary Tamm's performance as Romana (as well as a couple of stories with great scripts.)
Here are a couple of clips from Tamm's first appearance on the show, from "The Ribos Operation":
Click to view