Season 10
William Hartnell returned in a cameo as the First Doctor and Patrick Troughton in a more substantial role as the Second Doctor in The Three Doctors. This story marked the end of the Doctor's exile on Earth, opening up the series to more off-world adventures and beginning a gradual reduction of UNIT-related stories.
Episodes
1 The Three Doctors (1) Dec 30, 1972 
2 The Three Doctors (2) Jan 6, 1973 
3 The Three Doctors (3) Jan 13, 1973 
4 The Three Doctors (4) Jan 20, 1973 
5 Carnival of Monsters (1) Jan 27, 1973 
6 Carnival of Monsters (2) Feb 3, 1973 
7 Carnival of Monsters (3) Feb 10, 1973 
8 Carnival of Monsters (4) Feb 17, 1973 
9 Frontier in Space (1) Feb 24, 1973 
10 Frontier in Space (2) Mar 3, 1973 
11 Frontier in Space (3) Mar 10, 1973 
12 Frontier in Space (4) Mar 17, 1973 
13 Frontier in Space (5) Mar 24, 1973 
14 Frontier in Space (6) Mar 31, 1973 
15 Planet of the Daleks (1) Apr 7, 1973 
16 Planet of the Daleks (2) Apr 14, 1973 
17 Planet of the Daleks (3) Apr 21, 1973 
18 Planet of the Daleks (4) Apr 28, 1973 
19 Planet of the Daleks (5) May 5, 1973 
20 Planet of the Daleks (6) May 12, 1973 
21 The Green Death (1) May 19, 1973 
22 The Green Death (2) May 26, 1973 
23 The Green Death (3) Jun 2, 1973 
24 The Green Death (4) Jun 9, 1973 
25 The Green Death (5) Jun 16, 1973 
26 The Green Death (6) Jun 23, 1973