"Shada" is a rather infamous story for fans of Doctor Who, at least of the Classic Series. It was meant to be the final story of Season 17 and broadcast in 1980. Unfortunately, due to strike action, production of the story was interrupted and never completed. When Season 17 finished, it ended with "The Horns of Nimon" instead.
Over time, "Shada" took on an almost mythic quality. The more fans saw, the more they wanted to see. As a result, several versions of the story were released. In 1992, the surviving footage was released on VHS, with Tom Baker filling in the gaps via narration.
In 2003, a new audio/webcast version was released on CD and on the Doctor Who website. This version made a few small changes to the story due to featuring Paul McGann's Eighth Doctor rather than Tom Baker's Fourth, but it essentially remained the same.
But it was in 2017 that we were given perhaps the most definitive version of the story yet. This version included all the production footage, but it also completed most of the story via animation, with the original cast returning to voice their characters. On top of that, there was one newly recorded live-action scene...
"Such a nice old man"
The final scene features the Doctor working underneath the TARDIS console and talking about his friend Professor Chronotis - who, it turns out, was also a Time Lord criminal called Salyavin. After a small explosion occurs, the Doctor emerges from underneath the console...but looking a great deal older than before.
Yes, the final scene of "Shada" was recorded in 2017, with Tom Baker playing the Fourth Doctor in live-action once more. This wasn't the first time that Tom Baker had returned to Doctor Who on-screen - just a few years previously, he played the mysterious "Curator" in the 50th-anniversary special "The Day of the Doctor".
But seeing him play the Fourth Doctor again in costume - complete with that iconic multi-colored scarf - is really special. It doesn't make a huge amount of sense - the little explosion occurring seems to imply that it caused the Doctor to suddenly age, at least for a brief time - but then again, that really doesn't matter. The scene is a beautiful acknowledgment of exactly how long it took to complete this story.
Even better though is the dialogue. The story ends with the Doctor wondering what people will think of him in hundreds of years time.
"Is that really the Doctor? He seems such a nice old man."The Fourth Doctor (Tom Baker)
It's such a perfect line of dialogue. Even better is that this line wasn't added because Baker was older - the line itself was always a part of the script, and it was always meant to end the story. So having Tom Baker say it decades after leaving Doctor Who adds this wonderfully meta-layer of how time may have passed, but he will always be the Doctor. As a fan of his era, it is an emotional moment to watch.