A UFO hides in a lake on a country estate of a well-known equestrian, and the equestrian himself vanishes. When SHADO tracks down the UFO and manages to destroy it in an exchange of pot-shots, the UFO breaks up and leaves a thing floating in the water. Treated as if it is a bomb, it is brought back to SHADO and examined, with unexpected results.
A flashback episode in which Straker recalls his marriage, followed by stormy days as he must work covertly to get SHADO up and running and recruit personnel. All this leaves his wife angry at his absence, suspicious at the things he might be doing (her father photographs Straker meeting a woman in a parking garage, a woman who will be working at SHADO). In the end, she gives birth to their son.
The Master decides to sacrifice Jo to Azal and when the Doctor and his friends try to intervene they come under attack from Bok.
The Master orders Bert to set a trap for the Doctor at the village while a concussed Jo makes for the cavern.
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.
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.
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?
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.
A SHADO investigation reveals that romance may be complicating Moonbase operations.
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.
The Doctor descends into the Primitive city to try and find Jo while the colonists receive a visit from the Adjudicator.
Foster is suspected of being a security leak, but during the trial, Straker and his colleagues discover that Foster's apartment was bugged and shut down the disreputable business that is selling the spy gear.
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.
Hannibal Heyes and Kid Curry, two of the most wanted outlaws in the history of the West, are popular "with everyone except the railroads and the banks".
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.
Endora claims that Darrin has no sense of humor, so she puts a spell on him, turning him into a comedian. His client, Mr. Jameson, does not like Darrin's new Def Comedy Jam phase when he gets a migrane headache. Darrin discovers that Endora has hexed him, and she gives him another spell- this time, making jokes of anything sad or discouraging. The Jamesons come by and at th very mention of Jamison's wife's bursitis, Darrin starts laughing. Thinking that Darrin's insensitivity will cost Larry and him the account, the Jamesons think otherwise and give McMann and Tate the account.