Season 15
This season introduced K9 to the series and saw the departure of Leela. It was originally intended to include Terrance Dicks' story The Vampire Mutations but, due to a major BBC production of Dracula, it was postponed. It later became Season 18's State of Decay. To replace it, Dicks quickly scripted the season opener, Horror of Fang Rock. The season took a two week transmission break over the 1977 Christmas period, between the broadcast of part four of The Sun Makers and part one of Underworld.
Episodes
1 Horror of Fang Rock (1) Sep 3, 1977 
2 Horror of Fang Rock (2) Sep 10, 1977 
3 Horror of Fang Rock (3) Sep 17, 1977 
4 Horror of Fang Rock (4) Sep 24, 1977 
5 The Invisible Enemy (1) Oct 1, 1977 
6 The Invisible Enemy (2) Oct 8, 1977 
7 The Invisible Enemy (3) Oct 15, 1977 
8 The Invisible Enemy (4) Oct 22, 1977 
9 Image of the Fendahl (1) Oct 29, 1977 
10 Image of the Fendahl (2) Nov 5, 1977 
11 Image of the Fendahl (3) Nov 12, 1977 
12 Image of the Fendahl (4) Nov 19, 1977 
13 The Sun Makers (1) Nov 26, 1977 
14 The Sun Makers (2) Dec 3, 1977 
15 The Sun Makers (3) Dec 10, 1977 
16 The Sun Makers (4) Dec 17, 1977 
17 Underworld (1) Jan 7, 1978 
18 Underworld (2) Jan 14, 1978 
19 Underworld (3) Jan 21, 1978 
20 Underworld (4) Jan 28, 1978 
21 The Invasion of Time (1) Feb 4, 1978 
22 The Invasion of Time (2) Feb 11, 1978 
23 The Invasion of Time (3) Feb 18, 1978 
24 The Invasion of Time (4) Feb 25, 1978 
25 The Invasion of Time (5) Mar 4, 1978 
26 The Invasion of Time (6) Mar 11, 1978