5. The Keys of Marinus

After the sweeping vistas of 13th century China, we are now flung forward to far future on the planet Marinus. This time the TARDIS is being held hostage and the Doctor and crew have to retrieve 5 keys spread across the face of Marinus to get the TARDIS back. And thus the adventure continues.

Written my the creator of the Daleks Terry Nation, it was the only time the writer ventured outside of his creations. The Voord are actually quite interesting and could have been developed into a much more sinister adversary. But here they are not much more than background dressing and are sadly under utilized.

This story could have been told in 4 episodes but there is a bit of padding, with two whole episodes without the Doctor! Today those would be called "Doctor-lite episodes". In my timeline, I first watched season 16- "The Key to Time" which took the Doctor 6 stories to gather 6 pieces of the Key to Time. When I finally saw the Keys of Marinus for the first time, I saw the story roots of what became the Key to Time. In surveying the grand tapestry of stories that Doctor Who has woven over 50 years, I can appreciate this story's place in history and the foundation it laid for decades to come.

en.wikipedia.org/wiki/The_Keys_of_Marinus

Next thrilling episode- The Aztecs!!