Landmarks No.26

Logopolis.
The end of an era, as Tom Baker finally bows out after 7 years in the role of the Doctor.
It's the first story to properly feature the new Master - played by Anthony Ainley.
Nyssa becomes a companion - not just a guest character.
Tegan makes her first appearance.
Yes, the era of the over-crowded TARDIS begins here.
The TARDIS cloister room and its bell are introduced.
JNT gives us the first of the flashback sequences - allowing fans to see brief archive clips from the series within the narrative of the story.
Tom had played the Doctor for so long that it was hard to think of the programme going on without him. He is still synonymous with the role - his "look" being global shorthand for the Doctor to this day.
Ainley impresses from the first. He's not overused in this story - being an invisible presence for the first half. You can believe he is a new incarnation of the Master and not just being cast as a lookalike.
Nyssa also only features in the second half - brought to Logopolis by the mysterious Watcher.
Tegan is negative and argumentative from the outset - so we don't know if we are going to like her or not.
Knowing fans were starved of archive Doctor Who, JNT has the Doctor experience flashbacks of some of his recent enemies - and all of the Fourth's companions - as he prepares to meet his doom. Similar sequences will be included in Earthshock (previous Cyber encounters) and Mawdryn Undead (Brigadier adventures). All the companions bar Leela will feature in Resurrection of the Daleks.
There is a doom-laden feel to this adventure from the start. The Watcher is the second - and last to date - occasion where we see an intermediate stage in a regeneration (the first being Cho-Je / K'anpo). Barry Letts was involved with both.
After this story, Letts will not be associated with the TV programme again.