As of 2017, season 8 remains notable for being the season with the most number of regular characters. Not only did it see a new companion in the form of Jo Grant, but it featured a regular enemy — The Master — who was the first regular Time Lord enemy of the Doctor to appear more than twice, and an expanded regular UNIT cast that now included Sergeant Benton and Mike Yates in most episodes. Adding in returning regulars Jon Pertwee and Nicholas Courtney, the regular cast swelled to six.
When a Nestene Energy Unit is stolen and a radio telescope sabotaged, the Doctor is contacted by a Time Lord who tells him his old rival the Master is responsible.
2: Terror of the Autons (2)
Jan 9, 1971
Attempting to find out where Jo encountered the Master, the Doctor heads to the circus where he falls foul of Rossini.
3: Terror of the Autons (3)
Jan 16, 1971
The Doctor and the Brigadier head to Farrel's factory but the Master and the Autons have already left and are distributing plastic daffodils around the country.
4: Terror of the Autons (4)
Jan 23, 1971
The Doctor discovers the plastic daffodils are designed to fire a spray that asphyxiates people, causing havoc prior to the Nestene's arrival, but before he can alert anyone he and Jo are captured by the Master.
5: The Mind of Evil (1)
Jan 30, 1971
The Doctor and Jo head to Stangmoor Prison to investigate the Keller Machine, which drains the evil impulses from prisoners' minds, while UNIT are handling security at the first world peace conference.
6: The Mind of Evil (2)
Feb 6, 1971
The Doctor is recalled by UNIT to help investigate Cheng-Tiek's murder but is unaware that Chin-Lee is under the control of the Master.
7: The Mind of Evil (3)
Feb 13, 1971
Realising Chin-Lee has been using the power of the Keller Machine to carry out assassinations, the Doctor heads back to Stangmoor, only to find the Master has teamed up with Mailer to stage another riot.
8: The Mind of Evil (4)
Feb 20, 1971
With the Doctor and Jo being held prisoner, the Master convinces Mailer to help him steal the Thunderbolt.
9: The Mind of Evil (5)
Feb 27, 1971
The Doctor is forced to help the Master control the mind parasite while Yates finds out where the Thunderbolt has been taken only to be captured by the Master's men.
10: The Mind of Evil (6)
Mar 6, 1971
The Brigadier has recaptured Stangmoor but the Master still has control of the Thunderbolt and the Doctor must find a way to stop him and destroy the Keller Machine.
11: The Claws of Axos (1)
Mar 13, 1971
When a mysterious object lands near the Nuton power complex, UNIT investigate and encounter the Axons, a group of aliens who offer the mineral axonite, which can duplicate matter, as a gift.
12: The Claws of Axos (2)
Mar 20, 1971
The Doctor and Winser begin to analyse axonite while Chinn plots to secure its use exclusively for Britain.
13: The Claws of Axos (3)
Mar 27, 1971
The Doctor and Jo are being held prisoner by Axos while Chinn is forced to organise the worldwide distribution of axonite and the Master returns to the power complex to try and steal the TARDIS.
14: The Claws of Axos (4)
Apr 3, 1971
The Doctor and Jo escape from Axos but then the Doctor offers the Master a deal; if he helps him repair the TARDIS, they can flee Earth together.
15: Colony in Space (1)
Apr 10, 1971
The Time Lords take control of the TARDIS and the Doctor and Jo arrive on an Earth Colony in the 25th century, where a ruthless mining company are using a dinosaur-like creature to force the colonists to leave the planet.
16: Colony in Space (2)
Apr 17, 1971
The Doctor discovers an Interplanetary Mining Corporation ship has landed on the planet in order to mine its duralinium, while Norton begins causing trouble at the colony.
17: Colony in Space (3)
Apr 24, 1971
The Doctor makes it back to the colony and warns Ashe what Dent is up to but when Jo and Winton try to find proof they are captured.
18: Colony in Space (4)
May 1, 1971
The Doctor descends into the Primitive city to try and find Jo while the colonists receive a visit from the Adjudicator.
19: Colony in Space (5)
May 8, 1971
The Master offers to help the colonists in exchange for information on the Primitive city and forces the Doctor to act as a guide by taking Jo hostage.
20: Colony in Space (6)
May 15, 1971
The Doctor and the Master are taken into the Primitive city, where the Master hopes to find the doomsday weapon, while Dent forces the colonists to leave the planet even though their ship is likely to explode.
21: The Dæmons (1)
May 22, 1971
Earth, the near future. When an archaological dig at the village of Devil's End goes disastrously wrong, an ancient power begins to revive. Can even the Doctor withstand the power of the Daemons? And just what is the local vicar up to in his spare time?
22: The Dæmons (2)
May 29, 1971
With the Doctor frozen by the energy release from the barrow, Jo calls Yates and Benton for help, but when the Brigadier tries to join them he finds the village surrounded by a heat barrier.
23: The Dæmons (3)
Jun 5, 1971
The Doctor explains to his friends that the Master is trying to gain the power of the last of the Daemons, a race who influenced Earth's development, while the Master brings the rest of the village under his control.
24: The Dæmons (4)
Jun 12, 1971
The Master orders Bert to set a trap for the Doctor at the village while a concussed Jo makes for the cavern.
25: The Dæmons (5)
Jun 19, 1971
The Master decides to sacrifice Jo to Azal and when the Doctor and his friends try to intervene they come under attack from Bok.
