Season 12
All the stories in this season were interconnected, several forming a loose story arc relating to Space Station Nerva. The Cybermen returned to the series for the first time since The Invasion. Genesis of the Daleks, a story which introduced Davros and showed the creation of the Daleks, is one of the most famous of all Doctor Who serials.
Episodes
1 Robot (1) Dec 28, 1974 
2 Robot (2) Jan 4, 1975 
3 Robot (3) Jan 11, 1975 
4 Robot (4) Jan 18, 1975 
5 The Ark in Space (1) Jan 25, 1975 
6 The Ark in Space (2) Feb 1, 1975 
7 The Ark in Space (3) Feb 8, 1975 
8 The Ark in Space (4) Feb 15, 1975 
9 The Sontaran Experiment (1) Feb 22, 1975 
10 The Sontaran Experiment (2) Mar 1, 1975 
11 Genesis of the Daleks (1) Mar 8, 1975 
12 Genesis of the Daleks (2) Mar 15, 1975 
13 Genesis of the Daleks (3) Mar 22, 1975 
14 Genesis of the Daleks (4) Mar 29, 1975 
15 Genesis of the Daleks (5) Apr 5, 1975 
16 Genesis of the Daleks (6) Apr 12, 1975 
17 Revenge of the Cybermen (1) Apr 19, 1975 
18 Revenge of the Cybermen (2) Apr 26, 1975 
19 Revenge of the Cybermen (3) May 3, 1975 
20 Revenge of the Cybermen (4) May 10, 1975