The Doctor truly feels alone to me in this serial. Vicky, who felt like another incarnation of The Doctor's granddaughter Susan, was the last companion to travel with originals Barbara and Ian. To have lost all three, with no like-personalities to replace them (for Steven is a gung-ho shoot-first guy, a contradiction from Ian), you really get the first sense that The Doctor is a full-on nomad with no long-term connections to the universe besides their ongoing quest to simply go and do good. It's deeply sad, but it's also why I have watched for this long, about 13 or so years as of 2023. Having seen so many episodes on the other end, and having felt the depth of time between there and here, it's a massive gap and a tiny crack at the same time. The same basic issues of aloneness prevade.