It has to figure that with 850+ episodes in the books that there will be some that by some measure (content, context, or otherwise) qualify as unique. By classic definitions Mission to the Unknown taken on its own and not episode 0 of The Daleks Master Plan makes sense as it is that only story in the classic canon to be 1 episode only.
Today we celebrate the 14th Anniversary of possibly the most unusual episode of Doctor Who in the program’s history. 14th Anniversary you say? An episode from 2006 shouldn’t be considered thus, so the math doesn’t work in the context of nu-Who doesn’t it? But on February 29th, 1964 episode 2 of the William Hartnell historical Marco Polo entitled “The Singing Sands” was broadcast for the first and only time on BBC1.
Marco Polo is often cited as one of the most desired stories which are incomplete (or in this case completely missing) in the BBC Archives. Looking at the Tour’s gallery for the story it’s easy to see why. It looked simply sumptuous and, having listened to the audio for the story a few years back, would have been a great example of early Doctor Who at its best.
It’s kind of a shame that ‘The Timeless Children’ didn’t finish Series 12 a day early just to give ‘The Singing Sands’ some company, although we like the idea of having this day as a one-off. Perhaps we can try again in 2024.