Landmarks No.5

The Daleks' Master Plan.
Significant in so many ways.
For many years it was the longest running story (at 12 episodes). To be honest, it's really a 13 part adventure, Mission To The Unknown forming a Doctor / companion / TARDIS-less prequel.
This story will be chiefly remembered for the death of a companion for the first time. Poor Katarina (Adrienne Hill) came onboard in the previous story, but the production team had already realised that the character wasn't going to work. A character from ancient history would need everything explaining to them.
Hill's very first filming in the role was actually her airlock death sequence, on film at Ealing.
Viewers at the time would have been doubly shocked to see the apparent replacement, Sara Kingdom, also bite the dust before the end credits.
There won't be another companion death until poor old Adric in 1982, though it now happens with tedious regularity.
Episode seven - The Feast of Steven - marks the programme's first ever "Christmas Special" - in that it was broadcast on 25th December and is a bit of a stand-alone episode, with a high comedy quotient and a distinct lack of Daleks.
This episode also marks the first time that the fourth wall has been breached, as Hartnell includes all of us watching at home in his toast. I say first time, as it does happen a couple of times, less blatantly, in the Tom Baker era, when he addresses remarks directly to the camera with no other characters present.
Nicholas Courtney makes his début in the show, a few years before the iconic Brigadier Lethbridge Stewart. Courtney had earlier auditioned unsuccessfully for the same director (Douglas Camfield) but lost out to Julian Glover for the role of King Richard I in The Crusade. Camfield remembered him for the role of Bret Vyon in this.
The time-meddling Monk becomes the programme's first returning character (as opposed to a race of monsters).
This marks the late Raymond P. Cusick's final design work on Doctor Who.